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or epiphytic. The terrestrial species in the tropics are relatively 

 few. The epiphytes usually have thick fleshy leaves, and these 

 and their thick stems serve as storage organs, for their water 

 supply is precarious. While it is true that most orchids like 

 humid conditions, this is not always the case. During an 

 exploration of the Inaguas, which are extremely xerophytic, great 

 masses of Epidendrons were found growing on the bases of the 

 small shrubs or trees, or on the hot limestone rock ; and to 

 emphasize this desert condition, was a species of Agave growing 

 among them. They seemed to flourish, for the pseudobulbs 

 were strong and vigorous. 



Nearly all tropical orchids are epiphytic, while in temperate 

 regions they are terrestrial, the soil around their roots protecting 

 them from the extreme cold of winter. As a rule terrestrial 

 orchids have thin leaves, for their water supply is not so limited 

 as is the case with epiphytic orchids. 



In distribution orchids are very local. Few genera are com- 

 mon to both the Old World and the New, and when they arc 

 common to both, the distribuion is a zonal one. The genus 

 Cypripediiiui, as at one time understood, was a supposed excep- 

 tion to this. Recent authors, however, basing their conclusions 

 upon well-defined structural differences in the flowers, have 

 divided this, at one time cosmopolitan genus, into four genera, 

 each of the four genera with a well-defined geographical distribu- 

 tion. We have now, instead of the one big genus, the fol- 

 lowing : 



Selijiipidium, New World, with 3 species, known only from 

 Central America to Brazil. 



Cvpripcdiuin, Old World and New, but zonal in distribution, 

 with 28 species, north temperate. 



Phraginipcdiiivi, Old World, with i i species, in tropical 

 America only. 



Paphiopcdiliiin, Old World, with 46 species, tropical Asia, 

 Malaysia, Philippines, etc. 



As genera typical of a zonal distribution, there were mentioned : 

 Cypripcdmm, Pogotda, and Liuwdonun. Among the genera 

 peculiar to the New World are : Masdevallia, Pletirothallis, Epi- 



