3 oo SCIENCE PROGRESS. 



a single genus of flowering plants endemic in the Galapagos ; 

 but each island has its distinct species. Briefly put then, 

 the genera are the same in all the islands, and the genera 

 are American ; whereas a large proportion of the species 

 are peculiar to each island, though they are not so ex- 

 clusively confined to single islands as Darwin supposed. 

 On this point he says (41) : " Again Euphorbia, a mundane 

 or widely distributed genus, has here eight species of which 

 seven are confined to the archipelago, and not one found on 

 any two islands. Acalypha and Borreria, both mundane 

 genera, have respectively six and seven species, neither of 

 which genera has the same species on two islands, except 

 in the case of one species of Borreria." Dr. Baur's 

 recent explorations necessitate a considerable modification 

 of this statement ; yet in a sense they confirm and empha- 

 sise it. Baur himself deals more particularly with the fauna 

 (36) in illustration of this phenomenon. More than 400 

 specimens of the lizard genus Tropidurus were collected, 

 and in the result he found that "each island possessed only 

 a single species ; all the individuals of an island belonged 

 to one species ; and nearly every island had its peculiar 

 species or race ". 



The botanists who worked out Dr. Baur's collections 

 selected Euphorbia viminea (33) as an example of a plant 

 exhibiting racial differences in each of the eight islands, 

 where it is now known to occur. The genera Acalypha 

 and Borreria are cited as other instances. On the other 

 hand, Euphorbia articulata, which was collected on four 

 different islands, showed no such tendency. 



In a former article in this journal (32) I mentioned the 

 fact that huge branching Cactacese form one of the most 

 striking features in the lower zone of the vegetation of the 

 Galapagos, and I have elsewhere (42) given some par- 

 ticulars of what is known, and how little is known of these 

 Cactaceae ; and I may repeat here that specimens of only 

 one species have, so far as I can ascertain, been brought 

 away from the islands. These were brought to this country 

 by Darwin, and published by Henslow (43) under the 

 name of Opuntia galapageia. This species is remarkable 



