II. A METHOD OF DETERMINING THE ABUN- 

 DANCE OF SECONDARY SPECIES. 



RoscoE Pound and Frederic E. Clements. 



In determining the abundance of species, appearances are 

 extremely deceptive. One who has worked over the prairies 

 for many seasons comes to think that he can pick out instantly 

 the most abundant secondary species. Long continued obser- 

 vation in the field stamps a picture on one's mind, and it seems 

 a simple matter to pick out the several species and to classify 

 them in the several grades of abundance with reasonable ac- 

 curacy. As a matter of fact, this is not possible. After more 

 than ten years of active field work on the prairies, it seemed to 

 the writers that the mental pictures acquired was approximately 

 sufficient to make the reference of the commoner secondary 

 species of prairie formations to their proper grades an easy task. 

 When actual looking at the prairies as the season permitted 

 appeared to confirm the picture already formed, this seemed 

 certain. Closer analysis of the floral covering proved that the 

 conclusions^ formed from looking at the prairie formations and 

 from long field experience, without actual enumeration of indi- 

 vidual plants, were largely erroneous. The psoraleas, prairie 

 clovers and blazing stars would probably occur to all as among 

 the most abundant of the secondary species in the vernal, estival 

 and serotinal aspects of the prairies respectively. When we 

 first addressed ourselves to the task of assigning to each of the 

 various prairie species its proper degree of abundance, it oc- 

 curred to us at once that we could take a certain species, or 

 certain species, as types for each grade, and use these species 

 as standards by which to measure the others. It proved in the 

 end that the species selected, though of the commonest occur- 

 rence and hence familiar from daily observ^ation, were in many 

 cases referred to wrong grades as compared with other species, 

 no less common, but for some reason not so prominent. The 

 difficulty is that the species which appear most prominent in the 

 constitution of the prairies are not necessarily the most abundant. 



