124 Muhlenbergia, Volume 5 



In southern California it was first reported by McClatchie 

 in 1895 f rom Pasadena (37), and in the same year I collected it 

 along a street in San Bernardino, where its sparsity indicated 

 that it had probably first appeared the previous year. In a re- 

 cent interesting paper (38) Dr. A. Davidson relates finding, "in 

 the autumn of 1896, two plants in Los Angeles," and that the 

 same season Braunton had found it at Compton. Dr. Davidson 

 regards it as now "the most troublesome weed in the district, 

 and rivalling the mustard in luxuriance and density of growth." 

 At San Bernardino it has spread all over the valley, in waste 

 places and by roadsides, and in cultivated grounds and pastures, 

 but not on the dry mesas and foothills. It does not here exhibit 

 the extremely objectionable character attributed to it by Dr. 

 Davidson. While widely disseminated I have never seen it 

 growing densely, and seldom with luxuriance. The same re- 

 mark applies to the black mustard {Brassica nigra), to which 

 Dr. Davidson makes it a rival, and which is so dominating and 

 rank about Los Angeles, while with us it is but occasional and 

 produces little inconvenience. Evidently both weeds find more 

 congenial ecological conditions near the coast than in the drier 

 interior. 



When the prickly lettuce became fully established in the 

 prairie states it came to be recognized as the most aggressive 

 pest with which the farmer had to contend. In some places it 

 seemed that valuable farms would have to be abandoned be- 

 cause of it. But according to Dewey (39) the danger period 

 has passed. It "has either found natural enemies which keep it 

 in check, or for souk- reason it has lost much of its aggressive 

 character. It is becoming much less abundant in regions where 

 it formerly occupied nearly all the waste land and main- of the 

 cultivated fields, and the individual plants are generally less ro- 

 bust and less prolific than they weir six to ten years ago." 



:;; ) ]•"]. Pasad. 646. 

 38) Bull. S. Cal. Acad. <>: 17. [907. 

 1 39 1 Rhodora 7: 10. [Q< >> 



