Vor. 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, Zanthory- 
lum 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 Simarubaceae 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, T1911. 
