TAXONOMY OF THE HIGHER PLANTS 1 95 



of vascular plants. True, many species are represented by a single collection 

 and some by a single specimen. On the other hand, many species have been 

 studied in great detail and the assembled specimens of them number in the 

 hundreds, representing every known part of their geographical ranges. 



In modern taxonomic research, the specimens assembled over the years, 

 together with the published literature, form the starting point for a given 

 investigation. From the leads readily established from these two sources, the 

 student knows pretty well what the critical problems are and where he has 

 to go to find the material for their solution. His next step is into the field 

 to learn from the living plants. Here he comes to grips with variations of 

 every sort. The ephemeral, environmentally induced variations must be sorted 

 out from those of a more permanent nature that are of genetical origin. The 

 latter become the object of study from as many angles as possible. Gradually, 

 through intensive study, the taxonomist is able to discern constellations of 

 character combinations that run through his material. Some of these may 

 consist of variation patterns, others of characteristics without much variation, 

 or still other constellations may combine characters that display neat varia- 

 tion patterns and characters that are uniform. 



It matters little whether one studies species of plants, their constituent 

 parts, or genera and higher taxa, for the ultimate source of information is the 

 individual. And the individual must be studied as part of a dynamic popula- 

 tion of the same species which is forever changing because of the operation of 

 the particular genetic potential of that species. However, in spite of these 

 changes, it still retains the essential features that persist to distinguish it from 

 the nearest related species. Thus, we come full circle, returning to the prob- 

 lem of the sampling of a population and of a taxon. It is not a simple matter 

 to sample something of which we do not know the size, either as to the 

 numbers of individuals or the exact geographical extent. But this is the situa- 

 tion with most plant taxa. For that matter, the definition of a population is 

 extremely difficult, if not impossible, even when certain restrictions are im- 

 posed. Does a population consist of all the living individuals of a given species? 

 If one takes the affirmative view, he has to consider the fact that many species 

 have highly disrupted geographical ranges, with groups separated from each 

 other by hundreds or even thousands of miles. Neither the species with a dis- 

 rupted range nor even those with a continuous range are, to my mind, a single 

 population. Rather we tend to think of a population as being composed of 

 reasonably closely associated individuals, where interbreeding is freely pos- 

 sible. I am aware that such a definition is subject to criticism and that the 

 tropical botanist will point to the rather wide spacing of individuals of a 

 given species in a tropical forest. However, these spaced individuals are often 

 closely associated in terms of interbreeding because of the pollinating mecha- 

 nism involved. They share in a common gene pool. 



