458 J. LeConte — Flora of Coast Islands of California. . 



4. Lavatera, a remarkable malvaceous genus of which 18 

 species are known in the Mediterranean region, and one from 

 Australia, but not a single species on the American Continent, is 

 represented on these islands oy four species. This is certainly a 

 most remarkable and significant fact. 



Such are the facts. I account for them as follows : 



California, especially the region west of the Sierra Nevada, 

 is geologically very recent. The Sierra region was reclaimed 

 from the sea at the beginning of the Cretaceous, and the coast 

 region as late as the beginning of the Pliocene. When first 

 emerged the coast region was of course colonized from adjacent 

 parts. This colonization was probably mainly from Mexico, 

 either directly or through the Sierra region; for the distinct- 

 ively Californian plants, though peculiar, are more like those of 

 Mexico than any other. Whencesoever it may have been colon- 

 ized, however, the environment was sufficiently peculiar, the 

 isolation sufficiently complete, and the time has been sufficiently 

 long to make a very distinct flora. According to Wallace it is 

 one of the primary divisions of the Nearctic Region. 



During the late Pliocene and early Quaternary, as already 

 seen, the islands were still a part of the mainland, and the whole 

 was occupied by the same flora, viz : the distinctively Califor- 

 nian (with some differences doubtless), now found in both, to- 

 gether with the peculiar island-species. 



During the oscillations of the Quaternary the then western- 

 most coast range was separated by subsidence, and has remained 

 ever since as islands. Simultaneously with, or after, this sepa- 

 ration, came the invasion of northern species, driven southward 

 by glacial cold. Then followed the mingling of invaders with 

 the natives, the struggle for mastery, the extermination of many 

 (viz: the peculiar island species), and perhaps the slight modi- 

 fication of all, and the final result is the California flora of to- 

 day. But the island flora was saved from this invasion by iso- 

 lation, and therefore far less changed than the flora of the main- 

 land, i. e., the invading species are mostly wanting, and many 

 species survived there which were destroyed, or else modified 

 into other species, on the mainland, and the remainder prob- 

 ably less modified than on the mainland. The flora of these 

 islands, therefore, represents somewhat nearly the character of 

 the flora of the whole country during the Pliocene times. Some 

 modification they have doubtless suffered, but the time has been 

 too short for any great change in the absence of severe compe- 

 tition. 



The question naturally arises, "How is it that with a sepa- 

 ration of only 20-30 miles the two floras — insular and main- 

 land — have not become entirely similar by mutual coloniza- 

 tion ?" The prevailing winds being landward would, I sup- 



