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TEXTBOOK OF BOTANY 



Fig. 44. The largest of water lilies, Victoria regia, in bloom. Photo from New York 



Botanical Garden. 



20 feet long (Figs. 44 and 45). The century plant (Agave) has a type 

 of hard leaf with a heavy base and thickened blade, often variously 

 curved because of unequal growth (Fig. 46). At the time of flowering 

 the upper leaves of poinsettia are bright red. The leaf ( spathe ) that sub- 

 tends the flower cluster in the calla lily becomes white before the flowers 

 mature. 



Parts of leaves are sometimes so modified that it is difficult to identify 

 them as such. The stipules of the black locust tree develop as a pair of 

 spines at the base of the leaf. The stipules of pea vine are leaf-like, and 

 the terminal three or five "leaflets" are tendrils. On smart weeds the 

 stipules form a sheath about the stem, whereas on rose leaves they are 

 attached to the side of the petiole. The various species of asparagus have 

 only very small scale leaves; the leaf-like organs are branches of the 

 stem. All gradations between leaves and spines may be found on the 

 common barberry. Near the stem tip bud scales develop from primordia 

 similar to those of foliage leaves. 



