LEA VES: MOD I PICA TIONS 



93 



the desert, or the equally drying air of arctic or alpine regions; 

 third, where the normal functions of the leaf are combined with 

 some other utility; fourth, where the leaf is reduced to a very 

 small size on certain parts of the plant devoted to other than the 

 vegetative function (on the flower shoot for example) probably 

 according to the law of correlation; fifth, the floral leaves, the 

 sepals and petals of the flower, which are modified leaves with 

 usually loss of chlorophyll, and an adaption to other ends. 



149. Modifications where the normal work of the leaf is 

 lost. First, on underground stems like the mandrake, Solo- 

 mon's seal, the wake robin, etc., the leaves are reduced to mere 

 scales, are colorless, or at least lack 



the green color. The annual aerial 

 shoot bears the green leaves. Second, 

 in certain parasitic or saprophytic 

 flowering plants, like beech drops 

 (Epiphegus), the Indian pipe (fig. 77), 

 etc., the leaves, though on aerial 

 shoots, lack chlorophyll and are re- 

 duced in size to mere scales, the 

 plant obtaining its carbohydrate food 

 through its roots from its host, or as a 

 saprophyte, or with the aid of a fungus 

 mycelium in its roots. Bud scales 

 show another modification of leaves 

 from the normal function. Third, in 

 the cacti the leaves are supposed to 

 be reduced to mere spines since the 

 stem has taken on entirely the normal 

 function of the leaf. But in the barberry the leaves of the 

 main shoots are largely in the form of three rayed spines. That 

 these are leaves is seen from their position on the stem and the 

 fact that there are buds and shoots in their axils. 



150. Modifications of leaves in arid or arctic regions. 

 The leaf is greatly reduced in area so that there is a small amount 

 of surface exposed to the air in proportion to the bulk of the 



Fig. 78. 



Shoot of barberry showing 

 leaves modified to spines in the 

 axils of which a short shoot with 

 foliage leaves is developed. 



