FLORAL LEAVES OR BRACTS 195 



may disappear altogether, or become transformed into organs of a 

 different character. In one of tliesc forms the leaf becomes converted 

 into a s])ine, or a grou]) of s])ines, each consisting of one of the teeth. 

 In this condition the leaf serves an important function in protecting 

 the plant against destruction by desert animals. 



Phyllodia. — At other times the blade (Fig. 5().'^, a) entirely disappears, 

 a false blade (Phyllodium, Fig. 5()2), of much less activity as an evapor- 

 ating organ, becoming formed by the flattening out or exi)ansion of 

 the petiole (Fig. 553, c). A phyllodium is readil>- distinguished from a 

 leaf-blade in that its broad surfaces are directed laterally instead of 

 vertically, as in the true lamina. 



Leaves as Floating Organs. — Leaves or their petioles frequently 

 become luodified into floating organs in aquatic i)lants, as in the case 

 of the bladdery-inflated petioles of the Eichornia (P'ig. 504). 



Somewhat similar inflated organs exist upon the petioles of some 

 plants and serve as the homes of colonies of ants, which are efficient in 

 protecting the plant against the attacks of certain animals (Fig. 568, a). 



Leaves as Climbing Organs. — The office of climbing is frequently 

 ])crf()rnH'd by a portion of the leaf. In some cases, as the Clematis 

 (Fig. 569), the petiole of the leaf becomes twining for this purpose. 

 At other times the apex of the rachis (Fig. 567) becomes a tendril, 

 either simple or branching, while at others the entire leaf becomes thus 

 modified. In the Smilax (Fig. 565) it is the stipule which is thus 

 changed. In other cases (P'ig. 566) climbing is effected by means of 

 hooks develoi)ed u])on some ])ortion of the leaf. 



Floral Leaves or Bracts. — Besides protecting the i)laut by becoming 

 converted into spines or spine-bearing organs, as above described, the 

 leaf is subject to various other modifications having this object in view. 

 Ucfert-nce lias already been made to such modifications in the form of 

 bud scales. For the i)rotection of the flower exist the epicalyx and such 

 scales, called Floral Leaves or Bracts, as have been described in our 

 opening account of the flowers of the willow. 



Floral leaves or bracts do not always exist merely for jjurposes of 

 protection. In very many cases they are functionally a i)art of the 

 flower structure, surrounding either single flowers or clusters of 

 flowers, and ser\ing by their large size or brilliant coh)rs, or 

 both, to attract insect-\isits, i)rccisely the same as has be(Mi described 

 in reference to the i)erigone. Through the floral bracts thus modified, 

 we get a direct transformation into the ])arts of the perigone, as has 

 already been sufficiently explained. It is also important to note that 



