204 Elementary Biology 



The construction of nitrogenous compounds out of such 

 primary products of assimilation and the nitrogen salts ab- 

 sorbed by the roots forms the second stage in the process of 

 anabolism. At this point, however, the nature of the che- 

 mical changes involved becomes difficult to follow, and the 

 results of experiment and even of observation are anything 

 but beyond doubt. It is probable, however, that the com- 

 pounds of nitrogen unite with such compounds as formic 

 aldehyde, to form substances known as amides, the chief of 

 which in the plant is asparagin. These amides are then 

 transformed into proteids, and then into protoplasm, or into 

 protoplasm directly, by the action of already formed proto- 

 plasm. These changes take place quite independently of 

 sunlight and chlorophyll, which are necessary only for the 

 primary stages of anabolism. 



Circulation. We have already had frequent occasion 

 to assume the transference of substances from one part of 

 the plant to another. We must now glance at the methods 

 by which the food-stuffs in the plant are distributed through 

 the organism. 



Water is of course the great solvent in the plant, so that 

 the question of the circulation of food-stuffs really resolves 

 itself into a discussion of the movements of water. The 

 manner of entrance of water with salts in solution through 

 the root-hairs has already been considered under the head 

 of osmosis. The same principle holds good in the passage 

 of water with food- stuffs in solution from cell to cell. We 

 have to consider two types of plants, however, in dealing 

 with this question, viz. the vascular and the non-vascular. 

 In the latter the entire circulation is one of osmosis from 

 cell to cell, the cause of the movement being the disturbance 

 of the equilibrium between different cells by the removal, 

 by anabolic changes, of many of the substances undergoing 

 osmosis, the object of the movement being the re-establish- 

 ment of the equilibrium. Naturally this movement is a very 

 inconstant and irregular one. It also takes place in vas- 



