196 ROLLINS 



LOCAL POPULATION SAMPLING 



Real advances have been made in taxonomy in recent years by the develop- 

 ment and use of the technique of mass sampling of wild populations. This 

 is done by systematically collecting a large number of specimens in a set pat- 

 tern over a population. The specimens may consist of whole plants, or in most 

 instances they will be critical portions of plants selected because of a prior 

 knowledge of the type of data these portions will yield. Part of the data for 

 a population analysis will often be taken in the field. Items such as flower- 

 color variation, insect visitation, and other aspects of a given study must be 

 undertaken on the spot. And there are those who believe that the data for 

 a full analysis of a population should be gathered only in the field. However, 

 such a procedure has limitations. In the field, one cannot bring into full 

 play the aid provided by good microscopic equipment. Also of importance 

 are human limitations in the field. It is scarcely possible to assemble a full 

 complement of the kinds of variation data important in taxonomy from the 

 field alone. The most elite implications of variation patterns often are per- 

 ceived only after many comparisons of actual specimens, including critical 

 parts such as trichomes, pollen, stomata, cell structure, etc., and this can 

 best be done in the laboratory. 



Critical studies of living populations of plants and of mass samples from 

 them are now becoming a widespread procedure in taxonomic work. From 

 this type of study is emerging an ever-clearer picture of the complete nature of 

 plant species. Furthermore, deviations from expected patterns of variation 

 are showing up in increasing numbers. These are often traceable to the in- 

 volvement of special mechanisms of reproduction or, in many instances, to 

 natural interspecific hybridization. As the work proceeds, we may expect a 

 greater insight into the nature and extent of natural hybridization between 

 species and of such specialized reproductive mechanisms as those involved in 

 apomixis. 



NATURAL INTERSPECIFIC HYBRIDIZATION 



The impact of interspecific hybridization on classification, and particularly 

 upon the course of evolution, is only now coming into full view. Among other 

 things, the evidence calls for a recasting of ideas concerning the singularity 

 of the species as a key point in evolutionary differentation. The consequence 

 of reuniting once-separated evolutionary lines through hybridization is at 

 once evident. 



The fact that hybridization does occur naturally among plant species has 

 been widely recognized in plant taxonomy for many years, but there remains 

 much to be learned about this subject. The early and to some extent the con- 



