1919] Blasdale: Uredinales of California 103 



necessarj^ for their identification. Apparently an unusually large 

 number of Pacific Coast forms winter over, by means of uredineal 

 spores, and produce telia only occasionally and in very small amounts 

 or fail entirely to do so. 



Culture experiments are also greatly needed for the purpose of 

 ascertaining the specific identity of many of those species which 

 develop on closely related host plants, such, for instance, as the forms 

 of Puccinia which are found on the different genera of the Onagraceae 

 and Compositae. Such experiments in other regions have shown great 

 variability as to the closeness of the adaptation between the rust 

 and its host. In some instances, as illustrated by the classical work 

 of Eriksson and Hennings with the grain rusts, this relation is an 

 extremely narrow one and it becomes clearly necessary to recognize 

 species or subspecies based upon purely physiological distinctions. 

 It has been shown by Bethel, on the other hand, that certain species, 

 such as Puccinia suhnitens and P. stipae, produce their aecia on hosts 

 belonging to genera representing widely different natural families, 

 and it is not improbable that too much emphasis has been placed upon 

 the host plant as a criterion in ascertaining the specific limitations of 

 the rusts. 



III. PLAN OF THE PRESENT PAPER 



As one of the chief objects of the present publication is to assist 

 collectors in naming new collections and to tabulate all the known 

 forms and their accompanying host plants, the different genera, which 

 can usually be readily recognized if the mature form is at hand, have 

 been arranged alphabetically, and where a large number of species 

 are represented those species which occur on host plants belonging to 

 the same natural family have been grouped together and the groups 

 arranged according to the sequence of families found in Jepson's 

 Flora of Middle Western California. 



The references cited are designed merely to identify with certainty 

 the form referred to and to indicate where a description of it can be 

 found. Only those synonyms have been given which are necessarj^ to 

 show where certain species, whose validity is not accepted, belong in 

 the list. 



The data represented by the list is based almost wholly upon speci- 

 mens in the herbarium of the writer, and the name of the collector 

 of each specimen cited is given in parenthesis except where the col- 

 lection is that of the writer, in which case it is omitted. 



