222 CALIFORNIA ACADEMY OF SCIENCES. 



interval of time, and sometimes of a combination of both 

 causes. 



The intervening miles of restless ocean rendering the ex- 

 istence of connecting forms between a species of the main- 

 land and its insular form improbable, tends to give recog- 

 nized specific rank to forms which on the mainland would 

 hardly be considered good varieties and accounts for many 

 of the so called endemic species of islands. 



The direct effects of an insular climate upon vegetation, 

 with least intervention from other forces, are best shown 

 upon Santa Cruz and in the protected canons of Santa 

 Rosa. 



No general rule will apply to all plants, but different 

 species and genera seem to be variously iuliuenced by the 

 climatic conditions. 



As by far the larger part of the island flora is composed 

 of the maritime and Coast Range plants, species that delight 

 in ocean breezes, spray and fogs, it is not surprising 

 that many of them, in the midst of such conditions, 

 should often become very luxuriant. Of course differ- 

 ence of size is not a specific difference, but often this 

 insular luxuriance obscures the close relationship, which, 

 on that account, is sometimes best shown by insular de- 

 pauperate specimens, as in the case of Brodkea cwpitaia, the 

 Santa Rosa Grindelia, and other species. 



An interesting fact in connection with insular variation, 

 and one that is not easily accounted for, is the tendency 

 that mainland shrubs and bushes show on the islands not 

 to develop their lower limbs and branches and therefore 

 become tree-like. The most conspicuous examples of these 

 tree-like bushes are Pruniis ilici/olius, Cercocarpus, Rhus, 

 Rhamnus, Ceanothus. 



An insular form is not always a more luxuriant, but 

 sometimes is what may be considered a degenerate form: a 

 good illustration of this sort of variation is afforded bj^ 



