THE THEOKY OF WATEKING 213 



In other cases the discoloration is less intense, but the 

 elongation of the cells is so great that the epidermis is lifted 

 up into small wart-like protrusions on both the upper and on 

 the under surface of the leaf. 



The formation of yellow patches on leaves as described 

 above occurs in the leaves of Pandanus and Dracxna ; the 

 wart-like protuberances of the leaf surface may be observed in 

 Ficus elastica, Aralia, Hedera, Solanimb, and other plants. 



The appearance of yellow patches with indistinct margins 

 or of small glandular dilatations on leaves during the resting 

 period may be taken as signs that the plants are probably 

 suffering from a superfluity of water, and the watering should 

 be decreased. 



