560 



PHYSIOLOGY. 



small extent in which, by thunder-storms and electrical disturbances, it 

 is converted into nitrous acid, which latter becoming- oxidized, becomes 

 carried down to the soil as ammonic nitrate. 



A large proportion of nitrate is lost by drainage, and ultimately finds 

 its way into the sea, where it serves to nourish the marine plants, 

 which in their turn feed the animals. These latter, in decaying, yield 

 ammonia, the excess of which is volatilized into the air, which is thus 

 continually supplied with ammonia, and diffused over the surface of 

 the globe/ According to Schlosing, the ocean is the great source of com- 

 bined nitrogen, ammonia forming the means by which it is conveyed to 

 every part of the globe, supplying the requirements of the vegetable 

 world. Berthelot considers that the nitrogen may be acquired from the 

 atmosphere by electric action. 



Carnivorous Plants. One occasional source of nitrogen remains to 

 be spoken of, for though, according to our present knowledge, exceptional, 

 it seems probable that it is more general than it is at present proved to be. 

 For many years it had been known that some plants, such as Pitcher- 

 plants (Nepenthes), Sun-dew (Drosera}, Venus Fly-trap (Diomea), acted 

 as fly-traps, retaining insects which alighted on them, but it was hardly 

 supposed that these insects contributed to the nutrition of the plant. 

 The experiments of Hooker, Darwin, Tait, Vines, and others have, how- 

 ever, conclusively shown that insects and various animal matters are : 

 1, retained by viscid exudation, or, as in Drosera and Dioncea, by move- 

 ments of the/ leaf-lobes analogous to acts of prehension in animals; 2, 

 dissolved ; 3, absorbed ; and 4, appropriated to the requirements of the 

 plant. The shape of the Pitcher-plants -p i(r> 5 g 8j 



(Nepenthes, Sarracenia, &c.) is evi- 

 dently adapted to retain insects which 

 may 'be attracted on or fall into them 

 by accident ; and their conformation is 

 such as to prevent their exit, while their 

 intimate structure is such as to facili- 

 tate dissolution and absorption. The 

 lobes of the leaf of Drosera &c. are 

 endued with sensitiveness, so that when 

 an insect, or a piece of meat or albu- 

 men, and, still more, a fragment of 

 ammonia salt, comes in contact with the 

 leaf, the lobes in question instantly 

 begin to fold over and imprison the 

 intruding substance (fig. 588), which 

 gradually disappears, some or the whole 

 of it being absorbed a process at- 

 tended by retraction of the protoplasm 

 from the walls of the cell in the shape 

 of a ball (see fig. 590). It was further 



shown by Riess and Wills that the Leaf of Z>ro*em, showing the glandular 

 Solution of these nitrogenous matters hairs on one half infolded over an insect. 



is dependent on the presence of a substance which acts like a ferment, 

 and in the absence of which digestion does not take place. Gorup, 

 Besanez, and Vines have shown that this ferment closely resembles that 



