Volume I 1 Number 8 



The Plant World 



Jt ^Uaiiazinr nf (Ttrnn-al ?^atanp 

 AUGUST 1908 



TRANSPIRATION AND WATER STORAGE IN 

 STELIS OPHIOGLOSSOIDES SW. 

 By FoRRFST Shreve. 

 The work of Schiniper has shown that even in the most 

 pronounced tropical rain forests one may expect to find 

 xerophilous types of vegetation among the epiphytes which 

 inhabit the upper limbs of the tallest trees, while upon the 

 lower limbs and trunks may be found hygrophilous plants, 

 frequently including species which also grow in the deep 

 shade of the forest fioor. In savannas, or other tropical 

 regions with a low and well distributed rainfall, the wealth 

 of epiphytic vegetation is no less than in the rain forest but 

 is made up solely of the xerophilous types. The contrast in 

 the climatic conditions to which the high and low epiphytes 

 are subjected is as great as that which differentiates regions 

 of savanna and rain forest. P'or the high epiphytes there 

 is a brief period of rainfall each day, followed, or more 

 often preceded, by many hours of intense insolatIi)n, lowered 

 humidity and wind. For the low epiphytes there is shade 

 antl high humidity together with almost constant supplies 

 of water held by the beds of mosses and hepatics covering 

 the trunks and limbs. At mid-heights there are conditions 

 intermediate between these, an intermittent and uncertain 

 supply of water, together with conditions which are only 

 slightly less favorable to a high rate of transpiration than 

 arc those in the topmost limbs. I he xerophilous epiphytes, 

 like the perennial plants of the desert, fall into two classes, 



