SPECIAL FORMS OF LEAVES 



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59. Special Forms of Leaves. It has already been 

 mentioned that the parts of flowers and, often, thorns and 

 tendrils are like leaves in 

 origin. From this point 

 of view, such organs may 

 be described as " special 

 forms of leaves." It 

 seems much better, how- 

 ever, to discuss the parts 

 of flowers in the chapter 

 devoted to flowers than 

 to discuss them under 

 the present heading. 



As to tendrils, it may 

 be noted that the Vir- 

 ginia creeper is a familiar 

 plant whose tendrils arise 

 as leaves arise, while the 

 tendrils of sweet pea are 

 like leaflets in origin. 

 They show the same sen- 

 sitiveness to contact, and 

 the same general be- 

 havior as a consequence 

 of it, that has already 

 been noted in connection 

 with stem tendrils. In 

 the climbing nasturtium 

 the petiole often behaves like a tendril. 



As to thorns, the barberry is a commonly cultivated 

 shrub whose thorns are leaves as to origin. The thorns of 

 the locust trees are stipules as to origin. 



FIG. 88. View in a swamp showing the ver- 

 tical arrangement of leaves, which gives the 

 maximum amount of illumination for the 

 vegetation as a whole. 



