35/2 THE FUTURE OF ARID LANDS 
studies of the seeds found in adobe bricks from the walls of old 
buildings, including missions, whose construction dates are known. 
If time allowed, it would be interesting and enlightening to dis- 
cuss in detail the introduction and spread of weeds, species by 
species. Only a few can be mentioned, but these will serve to point 
up the problem. Hordeum murinum L. (common foxtail) is one of 
the most widely distributed grasses on range and pasture lands. 
Seeds were found in adobe bricks from missions constructed in 
1775 and in 1780. Brewer and Watson (3) reported it abundant in 
the south coastal area by 1860, in 1890 Hilgard (24) described it 
as a “fearful nuisance” in Central California, and in 1902 Davy 
(13) reported it rapidly coming in on the ranges of northwestern 
California. 
According to Robbins, twenty important alien grasses were 
fairly well established in the state by 1860. These include annual 
Bromus spp. and Hordeum murinum with obnoxious seed charac- 
teristics, and desirable annual species of Bromus, Avena, Lolium, 
Medicago, and Erodium. From 1860 to 1g00, Bromus mollis and 
several obnoxious annual Hordeum species became well estab- 
lished. 
The rapidity with which these alien annuals invaded an area is 
attested by Davy (13). From Sherwood Valley, Mendocino 
County, he gained an idea of the primitive flora. When the valley 
was first settled in 1853, Danthonia californica, a perennial bunch- 
grass, was the dominant and most valuable grass of the hillside 
and valley floor. In 1902 the prevalent grasses were Bromus race- 
mosus, Hordeum murinum, Festuca myuros, and A1ra caryophyllea, 
all introduced species except the latter. Reports indicate that one 
good forage grass, Bromus mollis, was not present in the state be- 
fore 1870, but in the short span of thirty years it was very abun- 
dant in most regions of the state (56). Talbot et a/. (66) again 
called attention to the “great extent to which the native vegeta- 
tion over vast areas in California has been replaced by plants 
introduced from the Old World.”’ 
What is the explanation for the rapid spread of these annual 
plants in California? They have proved to be extremely well 
adapted to the environmental conditions in the state, having 
superceded, under past and present management, the original 
