i62 LIFE : OUTLINES OF GENERAL BIOLOGY 



pounds for its own sustenance; but the difficulty is in regard to 

 nitrogen supplies, of which the moorland water has little. Thus the 

 sundew is "nitrogen-hungry", and hence the advantage of catching 

 insects whose tissues contain nitrogenous carbon compounds such 

 as proteins. As a matter of fact, the sundew can survive and even 

 seed without any insects, but Darwin's experiments, fully corrobo- 

 rated since, showed that plants fed with insects, fragments of flesh, 

 or particles of yolk of egg, flourished much better than those which 

 were left to themselves but shielded from insects. In some cases the 

 fed plants attained twice the weight of the controls, and produced 

 five times as many flowers and five times the weight of seeds. 



Allied to Drosera is the less highly evolved Drosophyllum lusi- 

 tanicum, common in dry, sandy, or rocky places in Portugal and 

 Morocco, and sometimes used by the peasants as a substitute for 

 flj-pajx^r. It has a better root-system than its marsh-loving allies, 

 and its long narrow strap-like leaves rise to a height of eight or ten 

 inches. They are interesting in being rolled up in the bud after the 

 fashion of fems, but backwards instead of forwards. They bear two 

 kinds of glandular hairs, stalked and unstalked. The former exude 

 a viscid gluey secretion which entangles insects, and besides this 

 a little formic acid. But they are not able to move like those of 

 the sundew. The unstalked glands secrete a digestive ferment, and 

 the stimulus comes from the capturing tentacles and also from the 

 formic acid which these secrete. Both kinds of glands share in the 

 absorption. The effectiveness of Drosophyllum may be inferred 

 from the fact that on one occasion the botanist Goebel counted on 

 a plant a year old, which had lived in a greenhouse with open doors, 

 no fewer than 233 distinctly visible flies, entangled on the surface 

 of nineteen leaves. Belonging to the same order, Droseraceae, is the 

 South African Roridula, in which the "insectivorous habit" is not 

 more than incipient. It may be regarded as a hint of a beginning. 



Vknls's Flytrap. — This native of the Carolinas was first 

 described (1768), in a letter to Linnaus, by Jolm Ellis, a London 

 merchant, who was one of the early students of corals. Linnaeus 

 called it miraculum Natures, and we cannot wonder. Like its 

 allies, the sundew\s, the Flytrap {Dioncea muscipula) lives in marshy 

 places. Its brightly coloured leaves form a prostrate rosette, from 

 the centre of which a stalk with numerous flowers rises to a height 

 of 4-() inches. Each leaf is a trap, consisting of a winged stalk and 

 a bilobed blade, the halves of which are movable on one another. 

 Round the margin of the blade are 12-20 long stiff processes, some- 

 what suggestive of a trap's teeth; and those of one side interlock 

 with those on the other when the blade closes. Rising from the 

 middle of each half blade there are three bristles, hinged at their 

 base, and they are espt^cially sensitive to the sideways touch of an 

 insect's feet. When the hairs are thus stimulated the halves of the 



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