20 



BOTANY 



k--. 



Honeysuckles. The blade of the leaf shows great variety of outline. 

 Some of the commoner types are shown in the illustration (Fig. 17). 

 Modifications of the Leaf. Leaves also show many adaptive modi- 

 fications. They may lose much of the green tissue and become 

 scales, such as enwrap the winter buds of 

 many trees and shrubs. These protective 

 scales are sometimes very large and conspic- 

 uous, as in the Hickory and Horsechestnut 

 (Fig. 18). Somewhat similar are the scale- 

 leaves of such bulbs as the Tulip and Onion. 

 Here the function of these leaves is twofold 

 protective and nutritive, as there is stored 

 up in them a large amount of reserve food. 

 Scale-leaves are usually derived from the leaf- 

 base, the petiole and lamina being suppressed. 

 This often shows in the transitional forms 

 which may be seen in an unfolding bud, where 

 there are sometimes all intermediate forms 

 between the scales and the perfect foliage 

 leaves. Scale-leaves of a somewhat different 

 nature are the rudimentary leaves of many 

 desert plants, and those of colorless parasites 

 and saprophytes, like Dodder or Indian-pipe, 

 where they are quite useless as organs of 

 assimilation. 



Bracts. A flower, or a group of flowers 

 (inflorescence), is often protected by more or 

 less modified leaves known as Bracts. Besides 

 FIG. 18. -Shoot of horse- their protective function, it is not uncommon 

 chestnut with winter r vi j * 



buds protected by i r bracts to become highly colored, and to 

 thick scale-leaves; k, take the place of the bright-colored floral 



leaves for the attraction of insects. The 

 Flowering Dogwood, Calla Lily, and many 

 Euphorbias offer examples of these showy bracts (Fig. 19, C). 



Leaf -tendrils. The tendrils of many climbers, instead of being 

 stem structures, may be modifications of leaves. These leaf-tendrils 

 are especially common in the Pea family, but are frequently met 

 with elsewhere. The tendril may be derived from the leaf-base 

 (Smilax), the petiole (Clematis), or the blade (Sweet Pea) (Fig. 

 19, B). 



Leaf-spines. The spines of Thistles, Barberry, and many other 

 prickly plants are modifications of foliar structures (Fig. 19, D). 



Insect Traps. Among the most remarkable of all plant structures 

 are the extraordinarily modified leaf structures developed by the 

 Pitcher-plants, Sundews, Bladder-weed (Utricularia), and others for 



