LEA VES : MODI PICA TIONS 



leaf to resist the trying arid climate of 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 cf 

 the plant devoted to other than the vegetative function (on the 

 flower shoot for example) probably according to the law of cor- 

 relation; 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. 



147. 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 cer- 

 tain 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 reduced 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 re- 

 duced to mere spines since the stem has 

 taken on entirely the normal function of foliage leaves is developed, 

 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 bud and shoots in their axils. 



148. 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 



