46 The Plant World. 



majority are phanerogams. The preponderance of ferns noticed 

 in the earlier expeditions had been lost, only six species of ferns 

 and one of Lycopodium being collected on the last visit. There 

 is now a remarkable scarcity of bryophytes. Two species of 

 mosses, but no liverworts, weie found by Dr. Campbell, and three 

 species of fleshy fungi have been collected. 



It appears that the earliest immigrants, bacteria, blue-green 

 algae, ferns and mosses, were wind borne, and the same is prob- 

 ably trui of the first phanerogams found upon the island, namely 

 composites and grasses; but later arrivals have been due in all 

 probability in a large measure to ocean currents, though birds 

 have doubtless played a part in bringing fleshy fruits, such 

 as those of Vitis and certain species of figs. The forest has di- 

 veloped so rapidly that it is to be expected that it will soon cover 

 the island again, as it did before the catastrophe of 1883. 



In a second installment of notes on introduced plants of 

 Southern California (Muhlenbergia, Oct. 23, '09), S. B. Parish 

 gives an account of the migrations of prickly lettuce {Lactuca 

 scariola L. var. integrata Gren. and Godr.), the Russian thistle 

 {Salsola kali, var. ienuifolia) and a number of other weeds, the 

 progress of which he has watched for some twenty years. The 

 interesting fact is recorded that certain weeds, such as Daucus 

 carota and Datura tatula, for example, which are very aggressive 

 and wide-spread on the other side of the continent, have main- 

 tained their foothold only for some years in Southern California 

 and have finally disappeared. As noted by Dewey, prickly 

 lettuce, which in the prairie states was recognized as the most 

 aggressive pest with which the farmer had to contend, is now 

 becoming much less abundant in regions where it formerly oc- 

 cupied nearly all of the waste land and many of the cultivated 

 fields, and the individual plants are generally less robust and less 

 prolific than they weie six to ten years ago. The frequency with 

 which this history is repeated in widely distant habitats indicates, 

 something of the exacting requirements which must be met in 

 the successful invasion and establishment of weeds which in 

 earliei years of their growth threaten to overrun the region into 

 which they have been introduced. 



