Vol. I] STEWART— BOTANY OF THE GALAPAGOS ISLANDS 215 



six of which are endemic. This family contains some of the 

 largest forest trees, as well as many herbaceous and shrubby 

 forms. All of these are most abundant in the dry and transi- 

 tion regions, and many of the species are armed with spines. 

 Several of the smaller Lianes being to this family. In the 

 moist and grassy regions the woody species are almost entirely 

 absent, but there remain a considerable number of herbaceous 

 forms, among which Desmodium is most conspicuous. 



The Rutaceae are represented by a single species, Zanthoxy- 

 liim Fagara, which occurs in all of the regions on many of the 

 islands. This species varies greatly in size, often occurring as 

 small bushes in the dry region, while in the moist zone it 

 assumes the height of a tree, the increase in size being gradual 

 with the increase in elevation. In many places in the dry and 

 transition regions this plant forms dense low thickets of bushes 

 which, owing to the strongly recurved spines that cover the 

 branches, are very hard to penetrate. It is one of the favorite 

 host plants for Phoradendron Henslovii on the parts of the 

 islands where this parasite occurs. 



The Simaruhaceae have but one representative, Castela gala- 

 pageia, which occurs as bushes in both the dry and transition 

 regions. This species varies greatly in the size of the leaves 

 and in the arming of the stem, so that several forms have been 

 based on these characters. 



Bursera graveolens and B. malacophylla are the only repre- 

 sentatives of the Burseraceae found on the islands. The first 

 of these is one of the most abundant forest trees in the dry 

 region, and is found on all of the more important islands of 

 the group but Duncan. It never occurs above the transition 

 region except as an occasional straggler. The second species 

 is endemic, and so far as known occurs only on the Seymour 

 Islands. 



In number of species, varieties, and forms, the Euphorbia- 

 ceae are the third largest family of vascular plants found on 

 the islands, and are of prime importance in that they furnish 

 many of the characteristic species of all of the regions. The 

 various forms of Croton Scouleri constitute conspicuous ele- 

 ments in all of the regions where this species occurs, and in the 

 dry region dense thickets of Croton bushes often cover consid- 

 erable areas almost to the exclusion of all other perennial vege- 



January 14. I9U. 



