PLANTS AND WATER 



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of light in a remarkably purposive fashion. 

 Thus nearly all the cacti, in their adult stages, 



Fig. 18. Taeniophyttum torricellense, an orchid with green, 

 flattened, leaf -like roots. R, roots; V, vascular strand; 

 F, flowering spike. (The roots are shown broken off at 

 the ends; they are actually much longer than indicated 

 in the diagram, which was made from a specimen in the 

 Natural History Museum, S. Kensington.) 



are destitute of green leaves, their stems 

 functioning as the photosynthetic organs. 

 Some of them, like the species of Phyllo- 



