Technical Information

Expand All    Collapse All

  • Definition of plant carnivory

    • Although many books have been written on CPs, until 1984 no-one had defined what constitutes carnivory in plants. The following definition is adapted from an article by T. J. Givnish and co-workers from Harvard University. This definition should be used in the future to avoid confusion.
      A plant must fulfil two criteria to be classified as carnivorous:
      1. It must have adaptations whose primary function is the active attraction, capture and/or digestion of prey.
      2. It must be able to absorb nutrients from dead animals juxtaposed to its surfaces, and gain some advantage from such nutrition in terms of growth, increased chance of survival, pollen production, or seed production. The first criterion is required to differentiate carnivorous plants from other plants that can passively profit from nutrients from dead animals decomposing in the soil or on their leaf surface. The second criterion is to exclude those plants that have defensive mechanisms capable of capturing and/or killing animals, but unlike carnivorous plants are unable to gain substantial nutrition from their prey. There are many plants that fulfil only one of these criteria, but which are not CPs. For example, flowers are effective in attracting insect pollinators, and some plants such as orchids temporarily trap insect pollinators to ensure pollen transfer. Other plants, such as members of the South African genus Roridula, trap and kill insects by their sticky resins, but apparently do not digest the prey. These plants do not fulfil all the criteria necessary to qualify as a CP.

  • How can plants move?

    • Venus Fly Trap
      Venus Fly Trap uses water pressure to move traps
      Drosera leaf wrap
      Sundew uses cell growth to wrap leaf around prey

      All plants have the power of limited movement, which may be as simple as the plant moving because it enlarges as it grows. But with CPs, motion can be extremely fast and striking. Since plants do not have muscle tissue, how do they do it? There are two main movement mechanisms that CPs use. The first kind of motion is what Venus Fly Traps (Dionea Muscipula) use to close their traps. It involves changes in water pressure. When the trap is activated (by touching trigger hairs on the leaves), the cells on the inside walls of the trap transfer water to the outside walls - essentially they become limp. This snaps the leaf closed. The second kind of motion is powered by cell growth. This action is triggered by detecting a touch sensation. On any plant having tendrils, the cell growth in the tendril takes place on the side opposite the 'touch' and so the tendril will, by default, curl around the touched object (epinasty), and hopefully provide physical support for that plant. The tentacles of sundews (Drosera) bend towards prey because the cells on one side of the tentacles grow. On the sundew many of the tentacles that move are not actually touched by the prey - it becomes a generalised action for the whole of that portion of the leaf. This is similar to the way bimetallic strips work in thermostats. Also in many of the sundews the rear surface of the leaf will grow, so that the prey is eventually 'wrapped' by the leaf. Incidentally, not all CPs have rapidly moving parts. Many, like the various pitcher plants for example, capture prey by forming very clever containers that creatures are lured into but cannot escape from.

  • Can I grow CPs in my garden?

    • Outdoor CPs
      Sarracenia grown outdoors.
      After reading the cultivation requirements, you tell me! Most people cannot. Most CPers grow plants in terraria or greenhouses. Some, however, dig holes in their yard, submerge plastic wading pools, and create backyard peat bogs. This can be a very rewarding exercise when properly installed - as explained in the outdoor bog section below. We are very fortunate in Victoria, and other parts of southern Australia, in that we live in a climate that allows many CPs to successfully grow and flower outdoors. Sarracenia plants are probably best grown outdoors, since they are less susceptible to fungal attack, and a cold winter dormancy encourages the plant to flower more readily. Cephalotus and Darlingtonia also appreciate the cooler conditions found in the open. Most Drosera and Utricularia species will thrive, although many tropical species are not hardy enough. Dionaea will also grow strongly; even many Pinguicula species, often noted for their tenderness, grow well unprotected. Rain and wind can have a stunting effect on some plants, but the only severe problem is snail, slug, and caterpillar damage. This can be controlled fairly well using baits, or the other suggestion for snails on the pests page. Plants grown outdoors are generally stronger and more robust, and often have a healthy look about them when compared to many greenhouse-grown plants.

  • What is hybrid vigour?

    • Hybrid vigour (or 'heterosis') is the phenomenon where a hybrid or cross shows an increase in such characteristics as size, growth rate, fertility, and hardiness over its parents, which are generally different from one another.
      Nepenthes hybrid
      Nepenthes hybrid (alata X spatulata) flowering outdoors in a cool temperate climate
      The first-generation offspring show these desired characteristics in greater measure. However, this vigour decreases when the hybrids are mated together until it becomes absent in about the eighth generation. Therefore if heterosis is to be used to its full potential, the grower must maintain the parental lines and make fresh crosses whenever a new batch of seed is required. Of course, such vigour will persist through vegetative reproductions. There is evidence that heterosis occurs in three of the 'hybridisable' genera of CPs, as far as is known. These are: Drosera, Nepenthes, and Sarracenia. Such characteristics in these hybrids make them easier to grow and more tolerant of temperatures usually outside the species' range. It is not known it heterosis occurs in Heliamphora or Pinguicula hybrids.

  • What is tissue culture?

    • Some growers prefer to avoid matters of compost entirely and propagate their plants on petri dishes in laboratory conditions. This is called tissue culture. Despite its peculiar nature, tissue culture is the best way to propagate some species rapidly. There are one or more members of VCPS (and usually some people on the net) who are involved with tissue culture, and you can meet them within the society. Many Pinguicula species and hybrids are distributed in tissue culture flasks, nowadays. As tissue culture plants have been protected for some months in their own sterile environment, when transferred from tubes, flasks, or other containers, they are susceptible to drying out, wilting, and attack from fungi.
      Drosera Prostratascaposa
      To ensure this doesn't happen the plants must be hardened off gradually while using a systemic fungicide. (Many fungicides have both curative and preventative action - the latter achieved by the residual activity of the product.) Once fungal activity has commenced, halting its spread requires stronger and more frequent doses of fungicide. It may be necessary to spray twice a week instead of one a week. To successfully transfer the flask plants to normal life in the outside world, the following steps should be undertaken. 1. Use hot water and add the recommended dosage of fungicide. Pour this over the compost and allow to cool. 2. Carefully remove all plants from the container and place them in a container of lukewarm water which contains a weak solution of fungicide. 3. Moving the plants around in the water will remove all the agar from the plants. The agar must be removed from each plant before planting it in the fungicide-treated compost. 4. Spray with the recommended dosage of fungicide every week for four weeks. 5. Place the container of plants into a high humidity and draught-free environment, for example a terrarium, or cover with a plastic bag. In this environment the plants should be shaded at least 50 to 90%, with humidity 70 to 100%, and a temperature of 19 to 25ºC (66 to 77ºF). After about two weeks the plants are able to cope with the temperature and humidity fluctuations and the lid of the terrarium can be lifted up slightly (or an opening made in the plastic bag). Relative humidity of 60 to 80% is adequate at a temperature of between 15 and 25ºC (59 and 77ºF). 6. Maintain this environment for a further two weeks, after which time the container can be placed in a greenhouse under normal conditions. High temperatures exceeding 30ºC (86ºF) should be prevented, as well as drying out of the plants and compost. If the plants are looking limp then prolong the period of hardening-off by two or more weeks until the plants look okay again. 7. After six to eight weeks the plants will be able to cope with more sunlight and can be grown just as you would for other plants of the same species.

  • What is Silicosis or Sporotrichosis?

    • Darlingtonia
      Darlingtonia californica
      Silicosis is a disease that is caused by inhaling particles of silica sand. The particles lodge in the lungs and irritate the tissue. Wearing a respirator when working with sand is advised. The following section discusses the disease Sporotrichosis found in Sphagnum in USA. Whilst enquiries so far have not found it to be present in Australia, it is wise to be careful. It would be quite rare, from experience and observation, for dry Sphagnum to be available or handled in Australia. Sporotrichosis is caused by the fungus Sporotrichum schenckii, which has been found in compost, flowers, shrubs, and even wooden mine props. Also found in Sphagnum. How the moss becomes contaminated is not clear, and attempts to detect the fungus in Sphagnum bogs have not been successful, but it has been found in bales arriving at nurseries. The fungus is found throughout the US, especially in Wisconsin. As of 1984, state forest tree nurseries no longer pack seedling trees in moss because of this. The Michigan USDA Forest Service nursery also discontinued the use of Sphagnum. Infection occurs when the spores of the fungus are introduced through a small abrasion or scratch in the skin. In one to four weeks a small painless blister develops at the entry site. This blister becomes inflamed and slowly enlarges. Other areas may become infected as the fungus spreads through the lymph vessels. Nodules may form along the infected lymph channels, and the lymph glands in the armpit or elbow may become enlarged and sore. If untreated, the disease progresses slowly to the bones, abdominal organs, and uninvolved skin. Diagnosed early, the disease can be adequately treated and is rarely fatal. Treatment is potassium iodine taken orally several times a day for up to three months. Expect upset stomachs. There is another treatment that has been developed which is preferred over this. Newer information indicates some uncertainty as to the fungal species. An article in the AOS Bulletin, indicated that New Zealand Sphagnum (once thought safe) can carry the fungus. The bottom line is, 'How contractible is this'? In CP culture circles there are MANY people who use Sphagnum extensively. Use a mask and gloves whenever you work with it, especially if you have any cuts or scrapes on your hands. Also use a mask and gloves whenever you are using any type of pesticide or herbicide, too. Regarding Sporotrichosis, an article written by Darroll D. Skilling, principal plant pathologist at N.Carolina Forest Experiment Station, 1992 Folwell Ave., St. Paul MN 55108, has been transcribed and summarised for the Carnivorous Plant Newsletter, March 1984. Have a search of the internet for a copy of this article.

  • Why are most CPs wetland plants?

    • Heliamphora
      Heliamphora heterodoxa
      In wetlands there are very few nutrients available for plants from the soil. Non-carnivorous species that live there have difficulty obtaining necessary nutrients and so do not thrive. CPs have found a different way to obtain nutrients, and so can survive. In environments with plenty of available soil-borne nutrients, CPs do not have this advantage. CPs are not well adapted to high nutrient levels, which is probably why they do not tolerate fertilisers and pesticides.

  • Why are these wetlands nutrient poor?

    • Drosera Ramellosa
      Drosera ramellosa
      In wetland environments where the water is not quickly recharged by streams, chemicals released by decaying plant matter can become concentrated. Some compounds, such as tannins, are acidic, and increase the acidity of the water. When the water becomes acidic, two things happen. First, many micro-organisms which aid in decomposition cannot function, so when plants die they do not rot - they just become waterlogged. With little decomposition, there are few nutrients for plants. Second, when the compost is very acidic, it is difficult for a plant to assimilate nutrients (which is why there are special fertilisers available for people who grow acid-loving plants). Both of these factors - decreased decomposition and the difficulty of obtaining nutrients from acid water - contribute to making wetlands nutrient-poor settings. Bog-water is sometimes so rich in tannins it is darker than well-brewed tea, but it is actually quite clean and odourless.

  • Pond, bog, swamp, marsh, fen - what are the differences?

    • People commonly describe wetlands with words like pond, bog, marsh, fen, and swamp, thinking these are mostly interchangeable. Actually, these terms are distinct and well defined. Ponds and lakes are all open bodies of water. For many people, a boggy place means an infertile wasteland, notable mainly for getting your car stuck and breading diseases like Malaria and Yellow Fever, but in fact a true bog is a marvellous living and growing 'organism' that is home for many species of CPs. A bog originates from a shallow fresh water source, such as a pond or small lake. In the northern parts of Europe and North America, glacial action has gouged out hollows that have filled with water from melting ice. Such glacial lakes have also been proven to be an ideal place for a bog to grow. A lake or pond shows signs of becoming a bog when Sphagnum moss starts to grow on the water's edge. This Sphagnum mat then proceeds to spread over the surface, while pieces may break off and become 'rafts' of floating moss. As the moss grows, it absorbs minerals from the water and replaces them with Hydronium ions, thus making the surrounding water very acidic (pH less than 7 (pH 7.0 is neutral - neither acidic nor alkaline)). Because of the thick mat of Sphagnum the water of such lakes soon becomes starved of oxygen. These conditions greatly retard the action of decay on organisms in the bog, so the sediments of dead plants that start to accumulate on the lake bed only partly decompose. Such sediment, comprising mainly dead moss that has fallen from the underside of the Sphagnum mat, mounts up and is eventually compressed to form a substance that we call 'moss peat'.
      CP pond
      CP habitat (Swamp)
      Bogs like these in their early stages of growth are often termed 'quaking bogs' because of their instability underfoot. Both men and animals have drowned in quaking bogs as they have ventured onto the seemingly firm bog, only to find themselves falling through the moss layer into the water below. Indeed this is the quality that distinguishes a bog from other wetlands: while bogs usually appear dry, marshes and swamps have standing water visible. Even in its early stages of growth a bog may be inhabited by heaths, stunted trees and, yes, even carnivorous plants! The damp acidic, and nutrient-poor Sphagnum raft proves to be an ideal place for a colony of sundews or pitcher plants (Sarracenia) to establish itself. CPs often predominate under such conditions as they can obtain from the insects they capture, the nutrients that are otherwise scarce in the mat where they are growing.
      Drosera stolonifera
      There comes a time when moss peat fills up the space between the floating Sphagnum and the original lake bottom. The bog may then be called a 'muskeg' with the arrival of a few scattered conifers like larch and black spruce. Although the bog may now be considered mature, it can continue to grow upwards if rainfall is sufficient to keep the raised moss moist. When a bog continues to grow like this it is called a 'raised bog'. Sometimes bogs can be formed by vegetation consisting of grasses rather than mosses, in which case they are called 'fens' or 'marl bogs'. Without the acid-producing properties of Sphagnum, the fen is usually alkaline (pH greater than 7), and is home to only a few tolerant CPs - such as Sarracenia purpurea and Drosera linearis. While bogs are not the natural environment for all CPs, various Sarracenia, Drosera, and Utricularia species could not grow under any other conditions. We therefore should take steps to preserve such bogs from destruction through agricultural and drainage projects, for a bog, just like any rainforest, consists of its own plants and animals, bound together by a unique ecosystem. Anyone who has seen a photograph of a large stand of S. flava or S. leucophylla in the wild will appreciate such a sight is unique to the Sphagnum bog and cannot be adequately substituted by plants in cultivation. Swamps are flooded forests. Places where the water table has temporarily (or seasonally) risen so the land is flooded, does not really constitute a swamp. Fens are usually considered to be places like bogs, but where the nutrient levels are higher. In different parts of the world other regional terms are used. Prairie is used in Okefenokee to describe floating Sphagnum or sedge mats. Savannah in the south-east US describes a grassy, seasonally wet meadow. In Europe, moors are peatlands usually dominated by Ericaceous shrubs (plants related to blueberries).

  • Build your own outdoor bog

    • Urtricularia
      Utricularia subulata
      An attractive and low-maintenance way to grow CPs outdoors is in an artificial peat bog. This effectively entails turning an area of garden into an environment that roughly duplicates the natural habitat of most CPs. In an area sheltered on south and west sides and receiving morning to early afternoon sun (preferable, but not essential), dig a hole ranging from about 25 to 30 cm (10 to 12") deep and about ten square feet in area. Line this with two thicknesses of polythene and place two 5 mm holes in the polythene in opposite walls about 15 cm (6") for drainage. The bog is then filled with a wet mixture of two parts peat to one of river sand, to within about 7.5 cm (3") from the top, and then about 5 cm (2") of one part peat to one part Sphagnum. Plant 30 cm (12") of 5 cm PVC pipe in the bog going from the surface down to about 2 cm from the bottom, and kept free of compost. To water the completed bog a hose is simply run down into this pipe and the bog can gradually be filled without disturbing or wetting the plants on the surface. The water level can be seen at any time by looking down the pipe, and hence the guesswork is removed from the question of when to water. The plants are planted in fairly natural-looking clumps; shorter plants in the shallow and more northern parts of the bog to give them adequate sun (not shaded by larger plants), while the larger plants have more room for their roots. A shallow polythene-lined pond can then be put in next to the bog to hold aquatic Utricularia plants - like U. australis. The bog can then be surrounded by suitable rocks. In winter the water level will probably be only a couple of centimetres from the surface due to rainfall; while in summer it will need to be watered weekly, to keep at least 5 cm (2") of water in the bottom of the indicator pipe. Such conditions will cause the Sphagnum on the surface to go wild, and it grows at such a rate as to soon fill the bog and start growing in a carpet up the sides of the rocks. Where easily-swamped plants such as small Drosera and Pinguicula grow, the Sphagnum must be cropped regularly to prevent overrunning these plants. Nevertheless, the masses of dense Sphagnum will make the bog look very attractive. The plants will propagate themselves and spread, there will be an established balance between the contesting plants, and before long every part of the bog will become a landscape of its own. The bog should also illustrate the large variety of insects that can be trapped by the CPs, in a number unknown in the greenhouse environment; while in spring and summer it will stun the observer with masses of colour. Growing CPs in an artificial bog can be easy and economical, and the resulting plants usually stronger and healthier than their greenhouse counterparts. It can make an inspiring project.

  • Do plants have a nervous system?

    • Venus Fly Trap leaf
      Venus Fly Trap leaf
      The Secret Feelings of Plants from New Scientist magazine - issue of 17 October 1992. by Paul Simons. Wouldn't it be nice to know that plants are more than just vegetables, that you can stroke them and they "feel" it? Heretical though it may seem, this thought certainly occurred to Charles Darwin who was fascinated by the Venus Fly Trap (Dionaea muscipula) and its response to touch. The way the plant snapped shut its trap seemed to him just like the response of an animal nervous system. Not having the equipment to test his outlandish idea, Darwin handed it over to John Burdon-Sanderson, an eminent medical physiologist at University College London. Burdon-Sanderson placed electrodes on the surface of the trap lobes and recorded something truly remarkable: each time a trigger hair was touched it fired off a wave of electrical activity akin to the nerve impulses, or action potentials, produced by animal neurons. Subsequent research showed that similar electrical impulses accompany the movements made by leaves of the "sensitive plant" (Mimosa pudica) in response to touch. Was this evidence that plants possess some kind of nervous system? Initially, botanists were sceptical. In animals, action potentials travel along nerve fibres at between 1 and 100 metres per second, whereas the impulses of plants rarely travel at more than 3 centimetres per second. Most damning of all, plants have none of the usual trappings of a nervous system: no networks of neurons, nerve fibres, or synapses. So how do they produce nerve-like signals? Today we know better. Building on experiments done in the late 1960s and 1970s, which confirmed that the impulses Burdon-Sanderson detected are indeed action potentials, plant physiologists are beginning to unravel the molecular and cellular basis of the ability of plants to respond to touch. Thanks to research at a number of American Universities in the early 1970s, it is now clear that the action potentials of plants travel not through specialised cells, wired up to communicate through synapses, but through ordinary cells - by means of microscopic membrane pores called plasmodesmata. Physiologists elsewhere have since discovered that many animal cells can pass action potentials through similar pores, known as gap junctions. The big drawback with both plasmodesmata and gap junctions is that they can only channel signals down one route. Once a Venus Fly Trap is hit, the whole trap is stimulated and only performs one movement. Compare that to an animal nervous system, which can respond to a given stimulus with any of the thousands of different muscles or glands in its body.

      The calcium trigger

      The main reason for this flexibility is the chemical versatility of the synapses through which the neurons communicate. When an action potential reaches the end of most nerve fibres, it cannot jump the synapse but instead releases neurotransmitters that diffuse across the synapse and trigger an electrical response in the neuron opposite. Using a variety of different types of neurotransmitters and neurons, a nervous system can process its signals like a hugely complex telephone exchange, constantly converting electrical signals into chemical ones and vice versa, and routing messages to different parts of the body. A plant cell communicating through plasmodesmata, by contrast, is much more limited in range and vocabulary: it can only pass electrical signals down one route and turn on one type of movement. But there are important similarities. As with neurons, these signals consist of currents of ions moving to and fro across cell membranes. Experiments in the 1960s showed that action potentials in the Venus Fly Trap, Mimosa, and similar touch-sensitive plants are all produced by currents of the same ions. In each species, a rapid influx of calcium ions into cells seems to trigger an action potential, and an efflux of potassium and possibly chloride ions appear to sustain it as it travels from pore to pore. The action potentials of neurons are produced in a similar way, but are usually triggered by sodium, not calcium. Considering its lack of specialised neurons and synapses, the Venus Fly Trap's response to touch is surprisingly sophisticated. During the late 1960s, Stuart Jacobson, an insect physiologist at Carlton University, Ottawa, discovered what appeared to be the equivalent of a special touch sensor in the flytrap. Each time he bent a trigger hair it translated the touch sensation into a localised electrical "code", in the form of a reduction in the voltage across the membranes of cells at the base of the hair. The harder the blow, the greater this so-called depolarisation, until eventually it reached a critical threshold and triggered the action potential that signalled the trap to close. Similar mechanisms seem to operate in Mimosa and the Venus Fly Trap's underwater cousin Aldrovanda. More intriguingly, many animal cells also possess sensors that convert mechanical stimuli such as touch into electrical signals, a prime example being the "hair" cells of the inner ear's cochlea which produce ionic currents when their hairs vibrate in response to sound. Coelenterates such as sea anemones and jellyfish have what is perhaps the closest thing in the animal kingdom to the neural system of the Venus Fly Trap - a nerve net where touch sensors, nerves, and muscles are all connected without synapses. The Venus Fly Trap and its relatives are no botanical oddballs. Touch-sensitive movements occur in more than a thousand species, spread across 17 families of flowering plants, and these, too, probably depend on electrical impulses. Research completed over the past two decades reveals that action potentials trigger the movements of Drosera (sundew) carnivorous traps, Mimosa, Biophytum, and Neptunia leaves. All of which leads to the question: if excitable plants are so widespread, are "ordinary" plants touch-sensitive too? Because most plants don't move very much, it is easy to assume they are not touch-sensitive. This assumption is wrong, as one American plant physiologist discovered. Mordechai Jaffe from Athens University, Ohio, started off in the late 1960s by looking at a familiar garden phenomenon - how pea tendrils coil around a support. Gently stroking a tendril a few times was enough to trigger the tendril's coiling, redirecting its growth from a fairly straight habit into rapid bending. Incomplete though the picture is, one thing is certain: touch-sensitivity in the plant kingdom is commonplace.

  • What is CITES?

    • Sarracenia
      Sarracenia leucophylla

      CITES stands for the Convention on International Trade of Endangered Species. This international agreement concerns itself with the shipping of endangered plants and animals. Many CPs are endangered, and so are under the jurisdiction of CITES. If you are trading plants internationally, you may need CITES permits. More information, including the document itself, is available on the Internet.

  • Preparation of carnivorous plants for postage

    • Nepenthes
      Nepenthes Mirabilis
      With the growing number of CP enthusiasts, more and more people are exchanging and selling CPs. Where distance is involved, it becomes necessary to send the plants by mail. This is standard practice for the suppliers that provide a mail-order service. It is quite a simple procedure to pack any number of plants of any size in such a way that they will arrive at their destination in the best possible condition. It is useless trying to send plants through the mail in large pots, as it only results in the plants becoming damaged. With some species it is possible to send the plants in a 50 mm propagating tube if it is packed in such a way that the contents of the pot cannot be shaken loose. This would entail packing some Sphagnum moss around the top of the pot and securing it. It will also be necessary to take steps to ensure that the plant is not damaged by the pot moving around in the outer container. The above method may be suitable for small numbers of small plants, but the extra weight of the pot full of potting mix (wet potting mix) generally makes it impractical as the postage charges are based on weight. So the more weight you have, the more you pay. A far better method is to send the plants bare-rooted, packed in a little damp Sphagnum moss, wrapped in a cling plastic - like 'Gladwrap'. This is packed into a suitable container (a small box or similar), and packed securely. The important point to remember is that there will be other mail on top of your container, so the container must be reasonably crush-resistant. For Sarracenia plants, a large box will be necessary, or you can use one of the many sizes of cardboard box or mailing tube available from Australia Post. It is a total waste of time and effort putting plants in a padded mailing bag, an envelope, or anything that will become crushed in the mail. The best methods of sending the plants are by Express Post delivery mail - this is very much essential. These services usually guarantee next day delivery anywhere in Australia, provided the parcel is lodged early in the business-day morning. The postage of such plant materials should be done on Mondays, Tuesdays, or Wednesdays; to make fairly certain that the shipments will not be sitting around in the postal system over a weekend. It naturally costs more than normal postage mail. It is also necessary to take similar precautions with the larger seeds (Sarracenia, etc.) as they can be easily crushed in transit or by the Australia Post sorting or cancelling machinery. Bubble plastic is probably the best packing material for seeds, and any spare space in your box of plants. If a large parcel of seeds is sent, then a padded post bag will be suitable. It is certainly worth the little time and effort, and the bit of additional postage cost, to make sure that the plants or seeds you are sending will arrive in the best possible condition. It is very upsetting to open a package and find that the contents have been destroyed in the mail due to careless packing.