118 THE NUTRITIVE FUNCTIONS. 



the other substances, including the different organic acids, 

 are restricted to certain plants. Here we must stop, for 

 we have not space for an enumeration, much less a descrip- 

 tion of the vast variety of vegetable products. Almost 

 every plant elaborates from the sap its peculiar solid, fluid, 

 and gaseous substances, which are connected in some way 

 or other with the final result of its vegetative acts, the de- 

 velopment of the future plant. We know nothing, com- 

 paratively speaking as yet, about the order in which these 

 substances are produced, their peculiar chemical relations, 

 or their physiological uses to the plant. The subtle 

 chemistry of the cell-laboratory, the way in which the 

 cells and tissues separately work, or the nature of that 

 composite influence which produces the future germ, all 

 this is very little understood. And let us not pride our- 

 selves on our knowledge of the economical uses of the 

 various vegetable products. Here also, science is in its 

 infancy. Those who think much of their attainments, or 

 imagine the subject ever has, or ever can be exhausted) 

 have never yet viewed it aright. They have yet to learn 

 the limited extent of human knowledge and the riches and 

 fecundity of nature. The finite mind can never fully com- 

 prehjend the works of an Infinite Being. The glorious sun 

 must pour all his rays into a twinkling star ; the illimitable 

 ocean be comprehended within a drop. 



It would seem that the nutritious portion of the sap not 

 required for development, is deposited in the cells in the 

 form of starch, which substance retaining its colorless ap- 

 pearance in the interior of the plant where it is excluded 

 from the light, is changed into chlorophyl in their leaves, 

 young shoots, and other superficial parts to which the 

 light has free access. Chlorophyl is a substance closely 

 allied to starch; and' appears to be equally nutritious to 



