THE PROBLEMS OF ECOLOGY 201 



several matters the systematist must look to the ecologist for help in 

 solving the most difficult problems of his field. In our present classi- 

 fication of plants there is still much that is artificial. On account 

 of the overwhelming number of species to be examined and placed 

 in the system, it has been as yet absolutely necessary to interpret 

 each chiefly by the historic type. Every thoughtful systematist 

 knows how arbitrary this is, and how seriously it hampers a natural 

 characterization of individual species. The majority of plants have 

 been first described from a very few specimens, or in many cases from 

 a single individual, which ever thereafter remains the type of the 

 species. That this historic type really represents the most typical 

 form of the species can only be a matter of accident. In many cases 

 it certainly does not. Yet, up to this time, it has often been impossible 

 to solve by purely taxonomic investigations the difficult question 

 which of several intergrading forms or varieties should be considered 

 typical, central, or original, and which are secondary, peripheral, or 

 derived. 



A complicated problem is here involved. It is true that it has 

 been somewhat obscured, although by no means hidden, by some sys- 

 tematists, who have thought to minimize the difficulty by the minute 

 subdivision of their species. This, however, is obviously only a matter 

 of words. To call a variety by a specific name does not stop its free 

 intergradation, nor solve the problem of its origin and variability. 

 It is certain that there are many variable species and that the varia- 

 tions have proceeded from a recent common type. It is further to 

 be inferred that this typical form is in many instances still extant, 

 but sure guides to its recognition are still a great desideratum in 

 systematic botany. The question is one of development influenced 

 by ecological conditions. It can be solved only by the closest scrutiny 

 of distribution and habitat, past and present, with relation to the 

 varying forms. Thus problems without number, of the greatest deli- 

 cacy, requiring the closest observation and soundest judgment, are 

 here opened to the ecologist who will turn his attention to questions 

 of geographic variation in polymorphous species. 



To turn now to a very different opportunity for successful work, I 

 would call attention to the rarity of what may be called experimental 

 ecology. It is not to be denied that some very interesting work has 

 been or is still being carried on along this line, as, for instance, Pro- 

 fessor Gaston Bonnier 's studies of the influence of altitude upon alpine 

 plants cultivated at different levels, but on the \vhole the field has 

 been little worked. Of course, it may be said that much of what is 

 classed as agriculture, horticulture, and forestry is a sort of experi- 

 mental ecology. But in these practical branches the scientific aspect 

 is apt to be obscured by the more conspicuous economic and aesthetic 



