36 OF THE ASSIMILATION OF CARBON. 



account is to be given of their form, structure, and 

 functions. 



When pure potato starch is dissolved in nitric 

 acid, a ring of the finest wax remains. What can be 

 opposed to the conclusion of the chemist, that each 

 grain of starch consists of concentric layers of wax 

 and amylum, which thus mutually protect each other 

 against the action of water and ether ? Can results 

 of this kind, which illustrate so completely both the 

 nature and properties of bodies; be attained by the 

 microscope ? 'Is it possible to make the gluten in 

 a piece of bread visible in all its connexions and 

 ramifications ? It is impossible by means of instru- 

 ments ; but if the piece of bread is placed in a 

 lukewarm decoction of malt, the starch, and the 

 substance called dextrine, are seen to dissolve 

 like sugar in water, and, at last, nothing remains 

 except the gluten, in the form of a spongy mass, 

 the minute pores of which can be seen only by a 

 microscope. 



Chemistry offers innumerable resources of this 

 kind which are of the greatest use in an inquiry 

 into the nature of the organs of plants, but they are 

 not used, because the need of them is not felt. The 

 most important organs of animals and their func- 

 tions are known, although they may not be visible 

 to the naked eye. But, in vegetable physiology, 

 a leaf is in every case regarded merely as a leaf, 

 notwithstanding that leaves generating oil of tur- 

 pentine or oil of lemons must possess a different 



