PLANTS OF PREY.

Auckland Star, Volume LV, Issue 170, 19 July 1924, Page 30

PLANTS OF PREY.

HOW INSECTS ARE CAPTURED. iRv Fawectt ClappL-rton, B.Sc.) A few days ago there .appeared in a -New Zealand contemporary a somewhat lurid account of a man-eating plant, said to have been discovered in America. While the details of the fearsome monfcter suggest the imagination of a modern Munchausen, there is yet nothing inherently impossible in tiie essential idea. Ii a very tiny plant can catch and digest an insect, a miu-li larger plant might catch and "cat*' a man. v.ho relatively is a far less powerful victim than a spider or an ant. AYe do not need to go outside ot" Xew Zealand t" !ind plant- that arc able lo perform the feat of capturing and consuming animal victims, and their means of doing so is as cunning and purposeful a; any that could be invented by ronian- ( in? travellers. The commonest of ii.cm is the Sun-dew (Drosp.ra), of which Xew Zealand has several species. It is an innocent-looking little plant, with leaves studded with shining glandular hairs looking for all the world like a feast of nectar spread for all insect comer.. But let this insect beware. The nectar is a fraud, a gummy trap from which, if the eager victim once touches it, it will not escape alive. In trying to rid its limbs of the sticky mess, it only makes matters worse : its breathing apparatus becomes choked, and finally, ■worn out with its struggles, it surrenders and dies. Meanwhile the tentacles upon the leaf have been moving towards the victim, gradually closing over it and emptying upon it a digestive fluid which in the course of a few days, dissolves the fleshy parts of the insect's body, leaving only the wings and chitinous casings. The gastric juice is re-absorbed, and the debris of the feast removed by the wind. The innocent looking leaf once more spreads the table and awaits the next unwary fly. The Sun-dew's Methods. The glandular hairs, or tentacles, are extraordinarily sensitive. Laing and Blackwell, in "Plants of New Zealand," mention the fact—presumably from Kerner's "Natural History of Plants" —that the four-thousandth part of a milligram of ammonium carbonate is sufficient to produce motion in them, while a piece of a woman's hair about two-tenths of a millimetre (i.e., less than one-hundredth of an inch) in length, placed upon a gland caused infection in the filament belonging to the gland. On the other hand it is said that if grains of sand, bits of glass or even sugar be dropped upon them no motion of the tentacles follows: This is a wonderful piece of discrimination, for the sun-dew in rejecting these substances appears to discover at once by a subtle sense that they contain no nitrogen, the substance which in every case insectivorous plants are striving to procure. Another remarkable point about the Sun-dew leaf is that not only is there a movement in the tentacles which have been touched, but that all the others do so as welL If the victim lands in the centre of the leaf, all the tentacles surrounding it curve inward, which means that a message was transmitted, as if by a nerve, from the point of contact to the untouched tentacles and, in answer, these move in a. purposeful way in the direction of the source of stimulus. They do not always move to the centre of the leaf, for, if two insects happen to be caught simultaneously, some of the tentacles tend towards the one, the rest towards the other. How the Bladderwort Acts. Besides the sun-dew group ther» is another New Zealand genus whose members are insectivorous. The bladderworts are mainly aquatic plants and | are so-named from the little bladders found along the stems. Filled with air they help to keep the plant afloat and its flowers above the water. But they hare also a more sinister purpose. To see their mechanism one must use both a hand-glass and a low-power microscope. The end of the bladder is found to contain a trap-door, easily opened from without, but not from within. Inside, tiny crustaceans may be found in all stages of decomposition. What led them to enter the trap is uncertain, but, once in, a cunning contrivance of hairs made escape impossible. Perhaps they were fleeing from a larger enemy and as the door of the bladder is protected by protecting hairs it as likely they sought it as a refuge into which their pursuers were unable to follow. Starved or Buffocated they soon died and the fluid part of the decomposing remains is now absorbed by special cells upon the inner walls of the bladder. Reversal of Nature's Usual Processes. What is th« interpretation to be put under these strange freaks of Nature? The thing that endears to us the humblest of all green things, evea the grass that clothes the fields, is that they do a lowly but fundamentally needful work for us with beauty. Even those that sting or tear do so in selfdefence. But the aggressive plaint which turns against those it should serve and devour them is a phenomenon that arouses at the best curiosity and more likely disgust. To explain it we have to get down to fundamentals. The main function of plant life in the general scheme of things is the manufacture of food, first for itself, and indirectly for the whole animal world. This it does by using the energy of sunlight for power; and air, water and the salts of the earth as raw material. The most highly finished produce of the pro. cess is the series of substances we call proteids. The exact composition of a proteid is unknown but it contains among other things the element nitrogen as an essential constituent. But' insectivorous plants grow where nitrogenous food material is scarce—in peat bogs or in stagnant pools. In tho struggle for a place in the sun they have found there competition less keen; but on the other hand the means to live made more difficult by the absence of any essential food. Necessity being the mother of dnvention, they have fashioned these wonderful means of getting back from animal life what originally and, shall we say, properly it is their function to give to animals. They have reversed the order of things. The descendants in all likelihood of fulltime primary producers they have escaped from the stress of competition and now batten upon those whom they ought to _ serve. They have attained "success in life," at a price: verbum sat sapienti.