ECOLOGY. 397 



only 48 species. These figures are for the genera as represented in 

 North America. 



It is believed that for most people a knowledge of the small number 

 of actual species will suffice for most purposes. However, in certain 

 lines of work the smaller units become of the first importance, espe- 

 cially in phylogeny and genetics. In consequence a system has been 

 devised in which these forms are treated as natural varieties or minor 

 variations of them and their relationships have been worked out in 

 considerable detail. By means of a series of phyletic diagrams the 

 degree of relationship is indicated between the various forms from the 

 variety to the genus. 



Special stress has been laid upon experimental and quantitative 

 methods as the only adequate basis for the synthesis of minor forms 

 into varieties and species. Consequently, much time has been given to 

 transplant and seeding experiments, and to statistical studies both in 

 field and herbarium. Exploration has been carried on for several 

 years throughout the West, and herbarium studies have been pursued 

 in most of the leading herbaria of the United States. Although the 

 work has been considerably delayed bj^ the endeavor to give the taxo- 

 nomic status of each segregate proposed its due consideration, the 

 monographs of Artemisia and Chrysothamnus are now completed, and 

 that of Atriplex is well advanced. 



Statistical Studies, by H. M. Hall. 



Quantitative methods are regarded as essential if taxonomy is to 

 advance from a descriptive to a true science. In order to aid in 

 bringing this about much attention has been given to certain genera 

 with the view of determining the amount of intergradation between 

 forms and the degree of difference where intermediate stages are now 

 wanting. The results have been used chiefly in arriving at conclusions 

 regarding relationships. The findings are consequently of the greatest 

 value in determining the proper taxonomic treatment of the species and 

 varieties of the genera mentioned above. For example, the results of 

 some 800 measurements of the style branches and appendages of 

 Chrysothamnus nauseosus have demonstrated by the computation of the 

 proper ratios that varieties gnaphalodes and hololeucus form a group 

 entirely outside of the other 22 varieties. The characters of these two 

 almost meet, but do not overlap those of the others. On the other 

 hand, the remaining varieties exhibit such irregular fluctuations in these 

 features that other characters must be employed in their classification. 

 Similar methods, involving determinations of the number of ray- 

 flowers, disk-flowers, bracts, etc., and the measurements of various 

 structures with the determination of their shapes, together with the 

 construction of graphs, have been of direct assistance in the study of 

 Artemisia, Atriplex, Chrysothamnus, and other genera. 



