BETTER ADAPTATION OF PLANTS 351 
tuation which could go in the direction of less productive types.”’ 
He emphasized that effective breeding work must be combined 
with a continuous improvement of the environmental conditions 
which man can influence. 
Although few genetic studies have been conducted on drought 
resistance, especially in forage plants, one can expect that genetic 
diversity exists just as it does for heading response to photoperiod 
and temperature in cross-pollinating species of Lo/ium. Similarly, 
there can be little doubt that self-pollinating species have a reser- 
voir of diversity in the homozygous biotypes that is available for 
selection by the plant breeder. 
Screening Procedures Leading to Selection of More Productive 
Plants for Arid Regions 
Before discussing screening procedures, I should like to describe 
briefly what has occurred naturally in California in the short span 
of 185 years. As a matter of record, great changes occurred in the 
floral composition of some parts of California in as few as 30 years. 
I believe this brief review will provide some interesting ideas on 
what might be done to improve the more rapid utilization of 
introductions and new types of plants. 
The majority of alien plants of California have been introduced 
unwittingly, and according to Robbins (56) “many have become 
highly undesirable, constituting our worst weeds.’’ According to 
Parish (54) “It will be safe, then, to assume a very definite date 
for the beginning of that foreign invasion which since has so 
greatly modified the plant population of the state. For it must 
have been a virgin flora that greeted the eyes of Fr. Serra and his 
companions, when, on the 14th day of May, 1769, they reached 
the bay at San Diego....The few previous explorers... had 
made but transient landings, but the followers of Saint Francis 
brought with them flocks and herds, and in the careful prepara- 
tions for their expedition they had been particularly charged to 
provide themselves with a store of seeds of useful plants... .” 
The first mission was established, then, in San Diego in 1769. 
The last of the chain of missions was built 800 miles to the north, 
near Sonoma, Sonoma County, in 1823. 
Hendry (20) and Hendry and Bellue (21, 22) made admirable 
