BETTER ADAPTATION OF PLANTS 347 
plots and seedings in California have demonstrated that EArharta 
calycina produces well in light soils in the 18-inch winter rainfall 
belt in the Great Central Valley of California, but on “‘tight”’ soils 
plants will survive only a year or two at the most. Phalaris tub- 
erosa var. stenoptera does very well on these ‘“‘tight” soils. In very 
sandy soils of coastal California the performance of E. calycina is 
remarkable, whereas P. ¢uberosa var. stenoptera survives only in 
the lower, more favorable, swale sites. This will be referred to 
again later. 
Many studies have been conducted, of course, on mowing or 
grazing effects on the capacity of plants to withstand drought 
conditions (64). In general, plants higher in food reserves are more 
tolerant of heat injury. According to Julander (29) large accumu- 
lation of colloidal carbohydrates, especially levulosans, is associ- 
ated with drought resistance. Heavily clipped plants do not 
accumulate food reserves during drought and are less resistant. 
It would seem, in summary, that physiological investigations 
on the nature of drought resistance should be intensified and cor- 
relative studies should be conducted on the sites and in the en- 
vironments where the range plants are used. 
Genetic Bases for Drought Resistance 
Olmsted (53) reviewed his work on photoperiodism of native 
range grasses of the midwestern United States. He found con- 
siderable variation, both interspecific and intraspecific, in their 
photoperiodic behavior. Intrastrain behavior also differed. A 
southern Texas strain of Bouteloua curtipendula showed less intra- 
strain diversity than the others. A strain from central Oklahoma 
exhibited the most intrastrain diversity in all respects, including 
photoperiodic behavior. 
Knowles (30) determined the extent of variation within Bromus 
mollis and the relation of this variation to the environment. An 
adventive species not present in California before 1870, it was 
abundant in most regions of the state by 1900 (56). In the short 
span of 70 years two distinct ecotypes are recognizable in Califor- 
nia: a late coastal ecotype and an earlier maturing interior ecotype. 
In addition, there is some genetic diversity within the ecotypes. 
Turesson (67) and Clausen, Keck, and Hiesey (5, 6) have done 
