316 Unii'crsitii of CaJifurnia ruhUcatianfi in Afiri<-nlinr<il Sciences | Vul. l2 



But, even though field studies of most of tlie species could not be made, 

 it was yet necessary to cidtivate them in order to study them cyto- 

 logically, and hence it has been possible to supplement the examination 

 of herbarium material by observations on cultivated plants which were 

 grown under fairly uniform conditions. By this method it has been 

 possible to show that certain characters (for example, nodding position 

 of the young flower heads) which have been used by some authors to 

 separate sections of the genus, are variable within a single species. 



Crepis was chosen in the first place because certain species have 

 small chromosome numbers and because the chromosomes are compara- 

 tively easy to study in some detail. A previous paper on chromosome 

 size and number in the genus (Mann, 1925) contained a majority of 

 the chromosome data herein considered, together with a suggestion as 

 to how a cvtologist would be tempted to group the species studied. Tn 

 this paper we have added somewhat to the cytological data and have 

 attempted to utilize both the cytological and the taxonomical modes of 

 attack. Generally speaking, this method has proved of the greatest 

 usefulness; and, while certain irreconcilable situations still appear to 

 exist, we have reason to hope that future developments — as we obtain 

 more species and make further studies — may show how such situations 

 have arisen and lead the wav to a clearer understanding of the genus. 



'>^ 



MATERIAL AND METHODS 



The species of Crepis upon which this study is based are all from 

 the Old World, and have mostly been obtained through the cooperation 

 of European botanists. Since we desire to make our study as complete 

 as possible, we shall greatly appreciate any assistance towards obtain- 

 ing viable seeds or roots of additional species. The taxonomic studies 

 have included the examination of both dried and living specimens, and 

 much care has been exercised in the determination of all this material. 

 The cytological methods were described in Mann (1925). 



Acknowledgments 



The investigations herein reported were conducted in part through 

 an allotment from the Adams Fund. It is with pleasure that we 

 acknowledge the assistance of Dr. J. L. Collins and Mr. C. W. Ilaney 

 in the growing of cultures and in providing us with certain data on 

 species hybridization. All the drawings were made by Helen E. 

 Rearwin, whose attention to accuracy of detail is gladly acknowledged. 

 0\ir thanks are also due to the curators of herbaria and directors of 



