72 



A TEXTBOOK OF BOTANY 



[Ch. Ill, 9 



or even when they are pinned up against a wall in the house, 

 as often done for a curiosity. Apparently this leaf is quite 

 genuine and not a stem in disguise, as one tends to infer. 



Finally, one often finds foliage leaves which exhibit ab- 

 normal features, such as forked, laciniate, crested, or even 

 pitcher-form blades, or eccentric coloration, or other unusual 

 features. When extreme, such cases are popularly called 

 freaks, and in science monstrosities. It happens that mon- 

 strosities in leaves are closely connected with those in stems, 

 and accordingly we can most conveniently discuss them to- 

 gether in a later section. 



9. The Forms and Functions of Leaves other than 



Foliage 



While formation of food is the primary, and usually the 

 exclusive, function of leaves some kinds perform addi- 

 tional functions, and exhibit corresponding peculiarities of 

 aspect and structure. Further, in some leaves the new 



function comes 

 to overshadow 

 the old, and 

 even to replace 

 it. In such case 

 we have a new 

 organ, though 

 one which re- 

 tains evidence of 

 its morphologi- 

 cal origin in its 

 mode of develop- 

 ment, and vari- 

 ous peculiarities 

 of structure. 



The simplest case of an additional function in leaves con- 

 sists in the storage of water or food, the presence of which swells 

 the leaves greatly, as in Century Plant, and Houseleek 



Fig. 44. — Mesembryanthemum obconellum, a plant 

 which stores water in the pairs of thickened leaves. 

 (From Goebel.) 



