246 



KNOWLEDGE. 



[November 1, 1900. 



There can be no doubt that the small animals thus 

 captured are an important part of the food-supply of the 

 Bladderwort; remains of as many as twenty-four cnista- 

 ceans have been found in a single bladder at one time. 

 Perhaps the most remarkable of the carnivorous plants 

 which capture their prey in this manner are the pitcher- 

 plants. In some of these the whole leaf assumes the 

 extraordinary pitcher-like form from which the plants 

 get their popular name ; in others, as in Nepenthes 

 itself, the pitcher is produced by a metamorphosis of the 

 leaf-stalk, the blade of the leaf being represented only 

 by a small lid which more or less covers the jjitcher- 

 mouth. There are about fifty species of these extra- 

 ordinary plants widely distributed in the warmer regions 

 of the eai-th. Of these about forty belong to the genus 

 Nepenthes, whose home is in the East Indian Archi- 

 pelago and the adjacent mainland ; there are also a few 

 species in Madagascar - and trojoical Australia. A 

 sjDlendid collection of living plants is to be seen in the 

 new Nepenthes House at Kew. Other genera are 

 represented in N. America (Sarracenia, Darlingtonia), 

 British Guiana (Hclianiphora), and Australia (Cephalo- 

 tus). The pitchers contain a fluid which in some cases 

 {e.g., Nepenthes) is poured into them from special secre- 

 ting cells in their walls; in others {e.g., Sarracenia) it is 

 partly if not entirely collected rain-water. They are 

 rendered attractive to insects, in some species, by a 

 honey secretion, and in most by a lurid veining of the 

 sides and top which is distinctly suggestive of animal 

 flesh. An insect once inside is prevented by various 

 devices from escaping, and death by drowning in the 

 fluid contents of the pitcher is therefore its fate. Its 

 remains simjjly rot in the fluid which is absorbed by 

 the plant, or in the case of some species of Nepenthes 

 their decomposition is hastened by an acid constituent 

 of the fluid produced by the ijlant itself and secreted into 

 the pitcher. Organic compounds derived from the bodies 

 of the animal prey are thus set free and are absorbed 

 into the plant and constitute an important element of its 

 food-sujjply. 



A second class of insectivorous plants is exemplified 

 by another well-known British plant, the beautiful little 

 Sundew, of which three species inhabit bogs and wet 

 places. These and several others to which we arc unable to 

 refer here exhibit movements of various kinds in the cap- 

 ture and '■ digestion " of their insect prey. In the common 

 Sundew {Drosera rotuvdifolia, Linn.), a small plant with 

 a rosette of leaves growing close to the sui-face of the 

 ground, the leaves are circular, from \ inch to A inch in 

 diameter and attached to the plant by long stalks. The 

 upper surface of the leaf is thickly beset by curious little 

 tentacles terminating in swollen reddish heads, which 

 secrete a colourless sticky fluid. This fluid, glistening 

 like dew in the sunlight, gives to the plant its popular 

 name. A small insect, attracted doubtless by the appear- 

 ance of honey, alights upon the leaf and "is unable to 

 extricate itself from the sticky exudation. Now occurs a 

 wonderful series of movements. || The tentacle or 

 tentacles touched by the insect slowly curve over until 

 the victim is thi-ust down between tliem upon the flat 

 surface of the leaf. At the same time all the tentacles 

 in the neighbourhood begin to curve and converge to- 

 wards the same point. The smothering of the prey is 

 thus complete, and its body is quickly decomposed bv the 



II In Brosophylbim hi.n/anicum, Link, a native of the PcninsuLi and 

 Morocco, the process of capture is the same as that dcscribcil frjr 

 Drosera, except tliat the stalked ghinds (tentaeU's) arc incapable of 

 movement. 



acid secretion poured upon it from the cells of the 

 tentacle heads. Its proteids are thus rendered soluble 

 and are absorbed by the leaf. In the case of Drosera 

 it has been experimentally proved that the plant thrives 

 better when it is able to obtain animal food than under 

 other conditions.^ These examjsles of the better known 

 carnivorous plants must suffice. They are so remarkable 

 that it is not unlikely that too much importance may 

 be ascribed to this curious habit. It must be borne in 

 mind that although some plants have adopted these 

 practices they represent but a very small jjart of the 

 immense group of green plants. This method of obtain- 

 ing Carbon and Nitrogen from the animal body is an 

 abnormal development which is of compai'atively little 

 importance in the jalant-world as a whole. 



THE GREAT TELESCOPE OF PARIS, 1900. 



By Eugene Antoniadi, f.e.a.s. 



It was at the initiative of M. Francois Deloncle, plenipo- 

 tentiary minister, that a group of amateur astronomers 

 decided upon devising for the Paris Exhibition an 

 instrument of exceptional size, far transcending anything 

 that had been before achieved in that line. With this 

 end in view, it was agreed to give to the object glass a 

 diameter of 49.2 inches, that is 9.2 clear inches more 

 than the Yerkes glass at Williams Bay, Wisconsin, and 

 13.2 inches more than the Lick refractor. Meantime, 

 in order to check, as far as possible, the defects 

 of spherical and chromatic aberration, it was resolved 

 to give the lens the immense focal length of nearly 200 

 feet. 



To mount such a leviathan on an equatorial foot would 

 practically be an impossibility. For to say nothing 

 of the tremendous weight of the tube, and the consequent 

 instability and flexures to which it would be exposed, 

 the protecting dome ought to have a diameter of at least 

 210 feet, thus surpassing by 72 the cupola of St. Peter's, 

 in Rome, and by 103 feet the dome of St. Sophia, Con- 

 stantinople. Owing, moreover, to the apparent diurnal 

 swing of the heavens round the Pole Star, the dome 

 ought, during observation, to be in constant motion, so 

 as to keep its opening constantly in front of the object 

 glass, speeding with a velocity of some 50 feet an hour ; 

 the eye-piece, too, would have to fly at a comparable 



/ // 



FlO. 1. — Principle of the Sidcrostat. 



pace, and it is needless to point to the inconvenience 

 to which the velocity of such motion would subject the 

 observer. 



^ F. Darwin. Journal of the Linnean Sociefi/, Vol. XVII pp ''S 

 andSOy. 



