SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 77 
The Changes in Our Weeds.* 
A. Davidson, M. D. 
In March, 1893, the writer published some notes of ‘‘Ery- 
threa’’ on the distribution and relative frequeney of the immi- 
erant plants in Los Angeles county. Nearly fourteen years 
have passed since then, and it is interesting to note the changes 
that have taken place among our weeds in this period of time. 
None of those then observed have become extinct; the relative 
frequeney of the majority have remained unchanged. Some 
have increased in numbers, and a few new ones have appeared. 
Among those on the increase are Melilotus alba Lam. and Cotula 
australis Hook. Bromus rubens L. & B. mamimus Desf. The 
former, rare and local at that time, has considerably increased 
in the original, localities, and may now be found in seattered 
patches in many parts of the country. Cotula Australis Hook, 
then limited to a single locality at Sierra Madre, is now to be 
found in many moist shady places along the public streets of 
Lios Angeles. 
Bromus rubens & B. Maximus have much increased, and have 
extended their range to the foothills of the Mojave Desert. 
The new weeds that have appeared since 1893 are, Salsola 
Kali, tragus, Galinsoga parviflora, Lactuca scariola, and Piaro- 
pus crassipes, Britton...Salsola kali. tragus, Linn., I first ob- 
served at Lancaster in 1893. It was then fairly abundant in 
the neighborhood, and rapidly spread over the country. The 
county supervisors have made a few spasmodic attempts to 
eradicate it, but it does not threaten to become a serious pest. 
Galinsoga parvifiora, first discovered by F. Braunton at Vernon 
avenue in 1903, has rapidly extended along the irrigation 
ditches into the southwest of the city, but is not troublesome. 
In the autumn of 1896 I found near University Station in 
this city two plants of Latuca scariola, L., the prickly lettuce 
of Europe. That same season Mr. Braunton reported it from 
near Compton, where it was quite troublesome in one place. 
Since that time it thas spread so rapidly that it may now be 
considered the most troublesome weed in this district. In 
luxurianee and density of growth it rivals the black mustard. 
On Sunset boulevard there is a large dense patch of mustard 
that has become invated by the prickly lettuce, and I am inter- 
ested in watehing which will ultimately predominate. As the 
mustard attains its growth in the spring and the lettuce in the 
autumn, it is possible they may both continue to thrive to- 
gether. Time will tell. Mr. S. B. Parish writes that he noted 
*Read before the Botanical Section Feb. 14, 1907. 
