ANGIOSPEEM^ 191 



ovary (Fig. 46, E). In such flowers the base of the 

 perianth is completely adherent to the ovary, so that 

 the outer part of the latter is completely fused with the 

 base of the perianth-tube, and the perianth appears to 

 be attached to the top of the ovary. Familiar examples 

 of this are seen in the various species of Narcissus (Fig. 

 46, E), Amaryllis, and other members of the Amaryllis 

 family. 



Much more profound modifications of the lily type 

 are met with in the Iris family. Here the cohesion of 

 the parts of the flower is accompanied by a suppression 

 of one set of stamens, and in some of them the flowers 

 are strongly zygomorphic, i.e. bilaterally symmetrical, 

 as in Gladiolus. The genus Iris (Fig. 46, F) is per- 

 haps the most specialized of the familj-, the peculiar 

 arrangement of the floral parts, especially the stamens 

 and pistil, being such as to render insect aid abso- 

 lutely necessary in order that pollination may be 

 effected. 



Some of the lily family reach the dimensions of trees, 

 showing a secondary increase in the thickness of the 

 stems, a rare occurrence among the Monocotyledons. 

 This is brought about, however, not by the contin- 

 ued growth of the primary vascular bundles as in the 

 Gymnosperms, but by a zone of growing tissue in the 

 ground-tissue, within which new vascular bundles of 

 limited growth develop, so that a section of the stem 

 of one of these arborescent Liliacese does not show 

 definite growth-rings, but appears as a mass of nearly 

 uniform parenchyma, in which are imbedded the 

 numerous isolated vascular bundles. The Yuccas of 

 the southern United States, and the Dracaenas and 



