222 The American Naturalist. [March, 
exerted the same influence? To this it can be answered that in 
places they are so protected, and Mr. Greene has mentioned in- 
stances where these insular forms still exist. These scattered 
localities are not regarded as points where the island genera have 
migrated to the mainland and there obtained a footing, but as pre- 
serving the same congenial influences which have made it possi- 
ble for them to survive on the islands. It seems to the author 
that the theory that the preservation of these scattered remnants 
of the old life is exactly what would result in places on the shore. 
They are remnants of a flora once widely distributed throughout 
California. 
These straggling colonies of characteristic insular flora are 
found, according to Mr. Greene, in isolated patches in San Diego 
and San Bernardino counties. These are supposed by him to be 
incipient colonizations on the mainland from the islands. Prof. 
LeConte, on the other hand, regards these patches as survivors 
of the Pliocene indigenes which have not followed the fate of 
their relatives, and the situation of these patches of older life in 
the southern counties, according to the latter, is “just what we 
might expect, for the main invasion [of hardy forms resulting from 
the influx due to the glacial cold] was from the north.” There 
seems no valid objection to considering these survivors as rem- 
nants of the flora of a former geologic period sheltered by envir- 
onment from destruction, but the causes which have led to the 
modification of their associates may not wholly be due to the 
influences of the glacial period. The other influence is conti- 
nental desiccation. 
The islands have, no doubt, been affected by the dessication of 
the continent, but not in the same degree as the mainland. Their 
fauna has changed, no doubt, since they were connected with the- 
mainland and the mammoth was found on both, but not to the 
same amount. The sea, with its fogs and local evaporation, has 
counteracted, in a measure, the drying up, which has been most 
marked at a distance from the sea. 
In conclusion, while accepting in the main the theory that 
glacial cold has had an influence, I would suggest that the main 
cause of the peculiar flora of Santa Cruz Island, observed by Mr. 
