142 PLANT LIFE 
cactus, often grown for the sake of their 
beautiful flowers, bear a strong resemblance 
to lobed, fleshy leaves. They are, however, 
merely stems, flattened by the action of 
light, which is probably indirectly operative 
through nutritive processes. If the phyllo- 
cacti are grown in the dark they only produce 
rod-like stems, very different from the leaf- 
like shape assumed under ordinary conditions 
of illumination. 
The cacti furnish a remarkable range of 
forms. All of them are pronounced xero- 
phytes. Now it is a curious fact that these 
plants of the Western hemisphere have their 
doubles in some of the euphorbias, or spurges, 
of the hot, dry regions of the Eastern tropics. 
So faithfully, indeed, are many of the leading 
types of cactus forms reproduced, that an 
untrained observer may easily be deceived. 
No satisfactory explanation has been given for 
the occurrence of these closely similar forms 
of plants, which are widely sundered in 
affinity and properties, as well as in their 
geographical distribution. 
The ordinary winter buds of our trees and 
shrubs, with their protective scales, provide 
us with still other adaptations by which loss 
of water from the enclosed leaves is prevented. 
The young leaves, since they are not only very 
thin, but are imperfectly protected by a cuti- 
cular surface, would assuredly suffer if they 
were exposed to the air. This is probably 
the chief function of the bud scales, though 
