CHAPTER V 

 THE PLANT 



The growth of plants is the result of a series of chemical 

 changes which first assume prominence in the sprouting seed, 

 with the ultimate object of producing seed for a succeeding gen- 

 eration. The effects of these changes become inconspicuous in 

 resting seeds, but their activity ceases only with the death of the 

 organism. 



Germination. A seed is essentially an embryonic plant sur- 

 rounded and protected by a supply of reserve materials which 

 serve as food until the young plant can forage for itself. These 

 reserve compounds are more or less complex structures involving 

 simple plant-food constituents derived from the air and soil. 

 The changes by which they are altered for the use of the seedling 

 are produced by sensitive compounds known as enzymes. 



These compounds are not endowed with life, but they are 

 probably closely related in composition to the complex, nitro- 

 genous compounds known as proteins, which form the basis 

 of living matter, and with whose chemical changes the life pro- 

 cesses of plants and animals appear to be very closely connected. 

 The exact nature of enzyme action is not known. One of the 

 older and more prominent theories of this action was based upon 

 the sensitiveness of these bodies and their proneness to undergo 

 decomposition. It attributed their effects to a sympathetic rela- 

 tion whereby they induced instability, or accentuated conditions 

 already unstable, in certain other compounds and caused them 

 to break down. This theory is insufficient for we now know that 

 enzymes can effect the construction, as well as the destruction, of 

 some compounds. Under proper conditions of temperature and 

 moisture small amounts of a given enzyme induce changes in a 

 large amount of matter, each kind of enzyme acting upon a 

 specific compound or group of compounds. Thus, a specific type 



