78 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



ated ; the blade is very thin, being composed of a 

 few layers of cells, and there are no stoniata. 



The basilar leaves and the apical leaves fre- 

 quently lose either partially or entirely the as- 

 similative function which they previously exercised. 

 Some of these leaves serve as a protection to the 

 buds of both leaves and flowers. Others are 

 adapted as protection from rain, and others have 

 undergone considerable modifications owing to their 

 existence either under water or under ground. 



In all these instances of modification it can be 

 seen that some degeneration has invariably attended 

 each change which has taken place. 



5. Modification of organs which are homologous 

 in individuals of different species. 



Having investigated the modifications of leaves 

 in the individual, we will now give our exclusive 

 attention to the various modifications undergone 

 by the foliage leaves ; we shall see among the 

 various species we examine that degeneration has 

 played a part in each instance of modification. 



Of these adaptations the following are the most 

 characteristic : adaptation to climbing, to a carni- 

 vorous diet, to aquatic life, to defence against ants, 

 against drought, and against herbivorous animals. 



1. Adaptation to climbing. Climbing plants 

 attach themselves by means of tendrils to the 

 nearest support within their reach. These tendrils, 



