118 BOTANICAL GAZETTE [AUGUST 
Since E£. crassifolium, a typical tomentose form, inhabits the 
San Diego region, and E. californicum, a glutinous form, the 
more humid central and northern California, it would indicate that 
a direct environmental influence was the causal factor in evolving 
the two types. That is to say, if specimens of the two types were 
grown under the same environment they would eventually become 
alike, but that is a point that remains as an enticing future problem. 
From the present studies, however, we learn that other members 
of the glutinous series occur in the San Bernardino Valley and even 
in the vicinity of Ensenada, Lower California, where they are 
subjected to more severe xerophytic conditions than are members 
of the tomentose type in the Los Angeles region. These distribu- 
tional facts demonstrate that the glutinous forms may be as well 
fitted to a xerophytic environment as those of the tomentose group. 
We may with equal propriety, therefore, suggest that the two groups 
represent two strains of a common stock that have developed 
independently. This theory is borne out further by the fact that 
forms of the two groups growing in contiguous territories more or 
less intergrade where they meet; while in isolated regions, where 
only one strain is represented, no marked variation occurs even 
in strikingly different environmental conditions. As an example, 
E. californicum is the only species represented on the Santa Cruz 
Mountain peninsula, while no related form extends north of the 
Santa Barbara region. On this peninsula various climatic condi- 
tions are at hand, and if the glutinous and tomentose types simply 
represent more or less xerophytic conditions, we should find some 
indications of the two strains; but such is not the case. Plants 
have been observed associated with the madrofio, California black 
oak, thimbleberry, and similar plants in mesophytic conditions, 
where the average annual rainfall is approximately 40 inches and 
where the rainless summers are ameliorated by frequent coast 
fogs. Other plants have been observed growing in typical xero- 
phytic chaparral, where the annual rainfall is less than half as much 
and summer fogs very infrequent. The only difference detected 
between the plants from these two stations was found in the stature 
of the plants and in the size of the leaves. 
