198 tN THE GUIANA FOREST. 



a contingency. Even the little pool of the Bromelia 

 does not last many weeks ; but not content with 

 that, the far-seeing plant has taken care to reduce 

 the evaporation from its leaves to a minimum and 

 made them hard and horny. In epiphytal ferns 

 moisture is stored in thick, leathery, or scaly 

 leaves, and in rhizomes of a similar nature. In 

 the orchids, however, we have the pseudo-bulb a 

 unique contrivance by which moisture is retained 

 through the longest drought. When the leaves 

 are thin they are often dropped, and the plant 

 becomes nothing more than a bundle of green 

 pseudo-bulbs attached to its support by a few 

 almost dry aerial roots. In this dormant con- 

 dition it rests quietly, and uses the store of 

 moisture simply for the purpose of keeping itself 

 alive. Other species have smaller pseudo-bulbs, 

 and thicker leaves, which are not deciduous these 

 rest somewhat, but never to the same extent as 

 the first Finally, we have species without any 

 means of storage except their thick, leathery 

 leaves, and these appear to endure drought with 

 less injury than the others. 



That these epiphytes air-plants, as they are 

 sometimes called are able to live in the way 

 they do, shows a marvellous power of develop- 

 ment in some past age. Some of them have 



