348 THE FUTURE OF ARID LANDS 
outstanding experimental work on plant ecotypes. Turesson 
showed that if collections of a species from different habitats were 
grown together under the same environmental conditions their 
distinctive characteristics are frequently heritable. Clausen et ai. 
by means of reciprocal transplants exhibited intrinsic differences 
between strains of wild species. 
Gregor and Sansome (18) and Stapledon (62) reported pros- 
trate habit of growth to be more common in coastal forms of 
bunchgrasses, but this appeared to be related to years of close 
grazing. Turesson (67) found the same situation in perennial 
dicotyledons from the maritime areas of western Europe. And 
Love (unpublished) found it to exist in Stipa pulchra, a native 
California bunchgrass. 
Love (35) reported that interspecific Stipa hybrids remained 
green longer than the parental species. These hybrids are sterile, 
and no doubt failure of seed production contributed to a longer 
period of green feed. He stated that it may become possible to 
interplant strains of two species which would cross and produce 
a population of vigorous hybrids interspersed among the parents. 
Technological difficulties involved in harvesting and processing 
Stipa seed have stopped this particular project. However, the 
fundamental idea may well be applicable to other closely related 
cross-pollinated species. 
Genetic studies with maize (Zea mays) were conducted by 
Heyne and Brunson (23) on the reaction of seedlings to high tem- 
peratures. In selfed lines and crosses between them, they studied 
linkage relations in eight of the ten linkage groups. Close associa- 
tion was found between heat tolerance and the Su su (sugary vs. 
starchy) and Pr pr (aleurone color) loci, and possibly including 
the Cc locus (color factor affecting Pr). Hybrid vigor had no effect 
on heat tolerance of the seedlings. 
Stebbins (63) reviewed his research work on interspecific 
hybridization of grasses. Since the production of new types by 
this process is a long and difficult process, he concluded: “‘If a par- 
ticular grassland region already possesses many productive 
forage species which are ideally adapted to it, the improvement 
achieved by this method is probably not worth the time and effort 
