I 66 PLANT WORLD. 



one In which there are merely structural pro^•isions for the 

 recluction of transpiration, and often for the external hold- 

 ing of water, as in the tillandsias, and a second in which there 

 are water storing tissues, as in many Orchidaces and 

 Piperaceae. Ihe Hrst class makes up the great bulk of the 

 epiphytic vegetation of the sa\'annas and the principal part 

 of that In the extreme top of the rain forest. The second 

 class predominates at mid-heights In regions with a heavy 

 and well distributed raintall. Here again there Is a close 

 analogy between the distribution of the two classes of 

 epiphytes and of desert perennials in relation to climate. The 

 epiphytes de\'oid of storage tissue are adjusted to regions 

 In which there Is a low but constant rainfall, while each day 

 presents to the water storing epiphyte a miniature duplica- 

 tion of the conditions which extend over many months for 

 the desert cactus. 



While making some studies in the montane rain forests 

 of Jamaica in iqo6 the attention of the writer* was attracted 

 by the rich assemblage of epiphytic types to be found there 

 and the exactness with which they are distributed In relation 

 to the vertical differences of climate in the forest. The 

 hygrophilous epiphytes of the lower le\'els are chiefly 

 Piperaceae and ferns, notable among which are numerous 

 species of Hymenophyllaceae. At mid-heights occur a few 

 species of water storing Plperacea and a rich representation 

 of OrchIdace;e, together with a few ferns and phanerogamic 

 plants which ha\'e no peculiarities of gross anatomy. In 

 the uppermost branches the Bromellace^E are represented by 

 a few species, of which one — Gitznuniui tricolor Ruiz & 

 Pav. — is very common, and with It grow a number of small 

 ferns and mosses, hepatlcs, lichens and blue-green algae. In 

 very many of the water storing . Orchldaceje the storage 

 tissue is located in the fleshy roots, while the leaves are thin, 

 as in Diclicica '^huica Lindl. and I), iriclioccirpd Lindl. In 



*Then holder of the Bruce Fellowship in the Johns Hopkins University. 



