FLORAL LEAVES OR BRACTS 195 



may disappear altogether, or become transformed into organs of a 

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

 into a spine, or a group of spines, each consisting of one of the teeth. 

 In this condition the leaf serves an important fmiction in protecting 

 the plant against destruction by desert animals. 



Phyllodia. — At other times the blade (Fig. 56.3, a) entirely disappears, 

 a false blade (Phyllodium, Fig. 562), of much less activity as an evapor- 

 ating organ, becoming formed by the flattening out or expansion of 

 the petiole (Fig. 553, c). A phyllodium is readily 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 modified into floating organs in aquatic plants, as in the case 

 of the bladdery-inflated petioles of the Eichornia (Fig. 564). 



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 

 performed 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 (Fig. 566) climbing is eft'ected by means of 

 hooks developed upon some portion of the leaf. 



Floral Leaves or Bracts. — Besides protecting the plant 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. 

 Reference has already been made to such modifications in the form of 

 bud scales. For the protection 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 purposes of 

 protection. In very many cases they are functionally a part of the 

 flower structure, surrounding either single flowers or clusters of 

 flowers, and serving by their large size or brilliant colors, or 

 both, to attract insect-visits, precisely the same as has been described 

 in reference to the perigone. Through the floral bracts thus modifled, 

 we get a direct transformation into the parts of the perigone, as has 

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



