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BOTANY: PRINCIPLES AND PROBLEMS 



original ancestor of all which have since evolved; and what has 

 been the cause of this steady and long-continued evolutionary 

 progress? The first question involves the origin of life, about 

 which we must frankly admit that our ignorance is still complete. 



Fig. 133.— The distribution of Gaylussacia dumosa (lined) and its variety 

 Bigeloviana (dotted). The species is characteristically southern, the variety 

 northern. In New Jersey and adjacent Pennsylvania, where their ranges over- 

 lap, the variety merges into the species, but in the rest of its range it is quite 

 distinct. Here we evidently have two groups of plants, within a single species, 

 which occupy different regions and which have diverged from one another almost 

 far enough to be regarded as two distinct species. (,Data from M. L.Fernald). 



The second, which relates to the cause and method of evolution, 

 is more nearly solvable and has been the subject of intense interest 

 and close study for more than a century. Indeed, it was our 

 inability to explain why and how evolution might have taken 



