316 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



Plant migrations. It seems probable that most of the indigenous 

 island flora is a remnant from the ancient land of Catalinia or reached 

 the islands by land bridges of the early Pleistocene. However, Holder 

 (1910) states that the Indians of the Channel Islands had certain 

 commercial relations with the mainland Indians. It is very possible 

 that there may have been considerable exchange of insular and mainland 

 floras through this intercourse. Millspaugh and Nuttall (1923, p. 220) 

 report possible circumstances by which Nicotiana glauca may have 

 been carried to Santa Catalina. In 1902 the chance combination of an 

 east wind with a large grass fire on the adjacent mainland was followed 

 by a greater increase in the number of Nicotiana plants the following 

 year. In view of the very small seeds of this species, the updraft from 

 the fire may possibly have carried the seeds high enough for the east 

 wind to have blown them to the island. While no examples have been 

 substantiated, birds have undoubtedly been an agency in carrying seeds 

 from island to island and also from the mainland to the islands, or vice 

 versa. 



That plants could be carried to the islands by ocean currents or by 

 prevailing winds seems highly improbable for two reasons: (1) land 

 plants or their seeds rarely survive submergence in salt water; (2) 

 both the prevailing winds and the ocean currents are generally directed 

 shoreward by the configuration of the islands and that of the mainland 

 coast. 



Due to the upwelling of bottom waters along the edge of the con- 

 tinental shelf off the coast of California, combined with the general 

 southeastern set of off-shore currents, the water about the islands, 

 probably largely bottom water, is clear and cool. As the prevailing 

 northwest wind passes Point Conception it veers more to the east, 

 following the east-west trend of the Santa Barbara coast. During the 

 late winter and early spring the southeastern drift of the ocean follows 

 the same general course, paralleling the coast. However, Tibby (1939, 

 pp. 13-14) reports that a reverse current seems to develop within the 

 borders of the continental shelf in the vicinity of the Tanner and Cortez 

 Banks, flowing northwesterly about San Clemente and Santa Barbara 

 islands. This current turns east in the Santa Cruz Basin and then 

 south to join the inshore current. Later in the spring the area of this 

 double reverse is increased and the northern drift includes the waters 

 about San Nicolas and the islands of the northern group. During the 

 summer a current, apparently originating far down the Baja California 

 coast, flows northward into the broad gap between Santa Catalina 

 and Anacapa. Here it divides, one branch flowing northwesterly about 

 the northern islands, the other turning toward the coast. 



