44 HEREDITY AND EVOLUTION IN PLANTS 



Nobody really knows. We have analyzed the substance 

 chemically, we have carefully examined and tried (but 

 without complete success) to describe its structure. We 

 know it is more than merely a chemical compound. It 

 is a historical substance. A watch, as such, is not. The 

 metal and parts of which a watch is made, have, it is true, 

 a past history; but the watch comes from the hands of its 

 maker de novo, without any past history as a watch. 

 But not so the plant cell. It has an ancestry as a cell; 

 its protoplasm has what we may call a physiological mem- 

 ory of the past. It is what it is, not merely because of its 

 present condition, but because its ancestral cells have had 

 certain experiences. We can never understand a plant 

 protoplast by studying merely it ; we must know something 

 of its genealogy and its past history. 



What is the origin of the sporophyte, and how did there 

 come to be two alternating generations? What is the 

 meaning of fertilization; what the mechanism and laws 

 of inheritance? How did there come to be on the earth 

 such plants as ferns? What was the origin of life? What 

 is life? No one can give complete answers to these ques- 

 tions; but the purpose of the study of botany is to help 

 fit us to seek the answers intelUgently. To those who are 

 interested in problems of this sort, nothing can be more 

 fascinating, nor more profitable. It is the aim of the fol- 

 lowing chapters to give a brief, elementary resume of the 

 method employed and the results obtained during the 

 past fifty years by investigators in their attempts to solve 

 two of the more important of these problems, namely, 

 the nature and mechanism of inheritance and the causes 

 and course of plant evolution. 



