t>ROSEBA ROTUNDIFOLIA. 341 



The aggregation is caused by various nitrogenous organic 

 fluids and salts of ammonia ; the most efficient agent for its pro- 

 duction being ammonic carbonate, .000482 milligram (73^^ of 

 a grain) being enough to cause aggregation in all the cells of a 

 tentacle. These figures show the extreme sensitiveness of the 

 tentacles and glands to slight external impressions. 



891. "If the glands are excited either by the absorption of 

 nitrogenous matter or by mechanical irritation, their secretion 

 increases in quantity and becomes acid." That it contains an 

 unorganized ferment admits of no question. The secretion after 

 excitation possesses the power of dissolving the albuminoids sub- 

 stantially as the gastric juice of animals does. When an insect 

 alights upon the leaf of Drosera, its violent struggles to escape 

 only wind more closely about it the threads of viscid matter 

 from the glands. Soon the tentacles close around it, and the 

 increased secretion of the digestive fluid brings about a true 

 digestion of the nitrogenous matter. 



892. That the digested matters can be absorbed, appears from 

 numerous experiments. In these, after the disappearance of 

 albuminous matters impregnated with a salt of lithium, it was 

 possible with the spectroscope to detect the salt in the plant. 

 Parts of the leaves remote from the seat of digestion, being 

 dried, calcined, moistened with hydrochloric acid, and placed in 

 the colorless flame of a Bunsen burner, gave the characteristic 

 lithium line. 



893. Does the plant gain any advantage by this absorption 

 of organic matter? Francis Darwin's 1 experiments upon this 

 subject may be briefly stated as follows : 



Two sets of thrifty plants of Drosera were cultivated under 

 the same conditions, with the single exception of a provision of 

 animal food to the leaves of one set. At the conclusion of an 

 experiment extending through three months, the ratios between 

 the unfed and the fed plants were as follows : 



Unfed. Fed. 

 Weight of plants, exclusive of flower-stems .... 100 121.5 



Number of flower-stems 100 164.9 



Total weight of flower-stems 100 231.9 



Total number of capsules 100 194.4 



Average weight per seed 100 157.3 



Total calculated number of seeds produced .... 100:241.5 

 Total calculated weight of seeds 100 : 379.7 



1 Journal of the Linnaean Society, xvii., 1880, p. 17. 



" Two hundred plants of Drosera rotundifolia were transplanted in June and 

 cultivated in soup-plates filled with moss during the rest of the summer. Each 



