BOTANY OF SANTA CRUZ ISLAND. 385 



where we know their seeds could have been driven across 

 the channel daring a winter's storm. The clovers also are 

 few, and there is but one peculiar species. But the whole 

 island is abundantly stocked with species of Hosackia and 

 Syrinaiium, which genera are exclusively West American, 

 and about half the species are peculiarly insular. Passing 

 to the Bosacece, we find the island totally destitute of such 

 cosmopolitan genera as Spircea, Fragaria, Potentilla and 

 Geum, of which there is no great dearth on the other side 

 of the channel; but the Calif ornian genus Heteromeles is 

 about twenty fold more abundant on this island than on any 

 equal extent of mainland territory; and Adenosfoma and 

 Cercocarpus, also Pacific American exclusively, are very 

 plentiful. Mr. Lyon in his very valuable paper/ has spoken 

 particularly of the fine wild cherry (Pranics occidentalis) of 

 Santa Catalina, which he fancies may be peculiar to that 

 island. It prevails quite as universally and is equally luxu- 

 riant on Santa Cruz. If there exists between this and its 

 depauperate congener of the Californian Coast Range, the 

 relation of parent and offspring, it must be that the insular 

 is the parent species. One of the principal moiphological 

 differences between the two is this: the leaves of P. occiden- 

 talis are ample and nearly or quite entire; those of P. ilici- 

 folia are, as the name implies, coarsely spinose-toothed, and 

 they are smaller. But the peculiar foliage of the reduced 

 mainland species is precisely that of all j^oung seedlings of 

 the insular, showing the case of the former to be one of ar- 

 rested development. The smaller size and the less palata- 

 ble and smaller fruit of P. ilicifoUa, are facts Avhich combine 

 well with its habit of retaining the foliage of the insular 

 seedling, to argue that the tree in migrating to our side of 

 the channel found in our mountains a soil and climate less 

 adapted to its full development. In confirmation of tliis 



1 Botanical Gazette, xi. 197. 

 26— Bull. Cal. Ac^D. Sci. II. 7. Issued May 28, 1887. 



