406 THE EVOLUTION OF THE SPOROPHYTE 



evolution, with all its wonderful diversities of form and struc- 

 ture in relation to insect life, diversities assumed to carry out 

 the relation of flowers to insect carriers of pollen. 



Part II of this work has given an outline of the evolution 

 and classification of plants based on comparative studies of 

 their morphology. The conclusions are necessarily speculative 

 and philosophical, for we have no means of knowing exactly 

 what has happened throughout the geological ages. The fossil 

 remains of plants are very helpful in certain groups, as the pteri- 

 dophytes and spermatophytes, but they are fragmentary and 

 relatively few, except for such periods as those when coal or 

 coal-like deposits were formed. Consequently our conclusions 

 as to the evolutionary history of plants must be founded chiefly 

 on studies of life histories and the comparative morphology of 

 living groups. In spite of difficulties, the plant morphologist has 

 been able to establish a classification of plants, based on kinship, 

 so as to determine the framework of evolutionary lines with 

 remarkable clearness, and these conclusions give to botany its 

 chief interest on the side of morphology. It is not strange that 

 the development of exact ideas in regard to plant evolution 

 should have lagged behind the progress made in that line in 

 animal evolution, since the paleontological evidence available for 

 the botanist, as above stated, is so scanty. It is only within a 

 very few years that any attempt has been made to introduce 

 beginners in botany to the evolutionary history of plants, and 

 popular knowledge of the subject is now no farther advanced 

 than was knowledge of animal evolution more than thirty 

 years ago. 



