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A TEXTBOOK OF THEORETICAL BOTANY 



covered a very great deal has been left out. The subject is so vast, in fact, 

 that only a few of the more important aspects could be touched upon. It 

 is not the policy of this book to discuss phylogeny or to enter upon the 

 thorny questions of the relationships of families with one another. From 

 what has been said it is clear that some families are closely related. In 

 many instances, however, the question of relationship is much more prob- 

 lematical and the personal opinions of individuals often outrun definite 

 facts. These are subjects into which we will not enter. They offer food for 

 thought and a student might do worse than reflect upon such matters and 

 attempt to formulate his own ideas. 



One thing is clear, however; the Dicotyledons and the Monocotyledons 

 represent two parallel evolutionary series. Whatever their ancestral form 

 may have been, and there are on that subject plenty of theories but few facts, 

 it is obvious that both the great groups have travelled forward side by side. 

 It is not surprising therefore to find a number of parallel adaptations or 

 modifications appearing in the two groups. These must not of course be 

 taken as indicating phylogenetic connections. In fact they serve as a 

 warning to those who would attach too much importance to floral structures 

 as a basis for deducing phylogeny. If two similar organs can be produced 

 by two clearly separate types of organisms, how much reliance can we 

 place on minor similarities as a basis of phylogeny. 



The following table prepared by Hutchinson will illustrate some 

 examples of this parallelism. 



