CHAP. III. FUNCTION OF NUTRITION. 211 



still continue to circulate for three or four hours in each. 

 By a strong electric shock, the force by which the latex 

 is propelled is paralysed, and its motion arrested. 



SIXTH PERIOD OF NUTRITION. 



(196.) Vegetable Secretions. In describing the pro 

 cess by which we have supposed the first step to be 

 made towards the organisation of those materials which 

 enter into the vegetable structure, we have considered 

 gum to be the immediate result of the fixation of car- 

 bon in combination with the two elements of water ; 

 and that this substance is formed by all those parts of 

 plants which almost universally acquire a green tinge. 

 We further stated that there were three other sub- 

 stances nearly allied to gum in chemical composition, 

 which might also be considered as destined for the 

 nourishment of the plant. It is probable that these 

 substances are only slight modifications of gum, produced 

 by its subsequent elaboration in the cellular tissue. It 

 is impossible, however, to point out the specific organs 

 which are appropriated to this office. In some cases 

 a distinct glandular structure is very apparent, and 

 the immediate secretions effected by it are collected in 

 an isolated form ; but in others there is no apparent 

 difference between the organisation of those parts in 

 which the secretions are produced and the rest of the 

 cellular tissue. 



(197-) Fecula. The first of the three alimentary 

 products which we shall further notice is fecula. This 

 substance forms minute spheroidal grains in the cellu- 

 lar tissue, and must be considered rather as a dis- 

 tinctly organised product than as a secreted matter. 

 Each grain consists of an insoluble pellicle or integu- 

 ment, containing a soluble substance which seems to 

 be pure gum, or some material scarcely differing from 

 it in any essential character. These grains are not 

 p 2 



