The Various Substances Made by Plants 129 



can not only produce and control chemical changes within its 

 own body, but, by pouring them out in suitable places, can dissolve 

 extraneous materials and later absorb these again for its own use. 

 It is thus that insectivorous plants can digest the insects they 

 capture; parasites can penetrate into the tissues of a host; and 

 pollen tubes can digest their way down the solid tissues of the 

 style, absorbing the digested materials for use in their own 

 growth. But there are many other phases of enzyme action also ; 

 thus the unfermentable cane sugar is hydrolyzed (or inverted) 

 to fermentable grape sugar by invertase, and grape sugar is fer- 

 mented to alcohol and carbon dioxide by zymase, produced by the 

 Yeast plant. And there are other cases innumerable which we 

 cannot take space to consider. 



Chemically and physically we know very little about the en- 

 zymes, because it has not yet been found possible to extract them 

 from the protoplasm in a pure state; and even their very existence 

 would not be recognized at all w^ere it not for their effects. It 

 is not even certain that they are related to the Proteins, although 

 there is indirect evidence pointing that way; nor are we sure that 

 they are liquids thinly saturating the protoplasm, though this 

 seems probable. Still less is it known how they produce their 

 remarkable effects, although a homologous power exists in those 

 inorganic substances called catalyzers. Each kind can produce 

 only one chemical change, and that as a rule but a slight one, 

 but the cooperation of several can cause a series of changes large 

 in the end; and it may be true that they cause most, if not indeed 

 all, of the chemical processes which the living protoplasm carries 

 on. They are the tools, so to speak, with which the protoplasm 

 effects the chemical results it requires. Indeed to some investi- 

 gators it has seemed likely that the enzymes are the principal 

 material bases of heredity, and that the chromosomes of the 

 nuclei, known to be conveyors of heredity, consist chiefly of col- 

 lections of enzymes. Truly the importance of the enzymes is 

 great, and their further study in the near future is likely to throw 



