136 Robinson and Greenman— Galapagos Flora. 
forms than Luphorbia viminea Hook. fil. This species differs 
markedly in foliage from any other known member of: this 
large genus, and is characteristic of the Galapagos Archipelago. 
Being essentially a desert plant, it can subsist even upon those 
islands of the group which are of low altitude and do not 
attain the upper regions of moister atmosphere. It was first 
collected by Macre upon Albemarle, rediscovered by Anders- 
son on Charles Island, and has now been collected by Dr. 
Baur upon the following islands: Barrington, Chatham, South- 
ern and Eastern Albemarle, James, Jervis, Bindloe, Tower, an 
Abingdon. Even the most cursory inspection of the forms from 
these different islands discloses marked variation in the contour, 
size, thickness, rigidity, and color of the leaves, as well as im 
the length of the internodes, color of the stems, etc., while 
more careful examination shows that these are not mere indi- 
vidual differences, due to chance, state of development, or indi- 
vidual environment, but each form appears in general to be 
restricted to a single island. Some forms, such as those 0 
Abingdon and Tower Islands, differ rather strikingly from the 
rest, while others present slighter differences; in a few cases 
so slight, that a series of careful measurements is necessary t0 
demonstrate their existence. But the examination of a con- 
siderable number of specimens, such as those secured by Dr. 
Baur, shows that the species, as it occurs upon each island, 
composed of islands of elevation, built up from the sea-fo0r 
independently by voleanic action, how has such a distribution 
been effected. If the vegetation has been derived from the 
mainland by the chance transportation of seeds, it 18 quite 
impossible to believe that each island has received a slightly 
different form of the same species, and we are forced to ° 
more natural, seed must have reached one or more 0 he 
islands and from these spread to the rest. That the same 
species should have reached all these islands presupposes 4 ¢0”” 
Sere eee oer y 
