ANGIOSPERME 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, #.e. bilaterally symmetrical, 
as in Gladiolus. The genus Iris (Fig. 46, F) is per- 
haps the most specialized of the family, 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 Liliacee 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 Dracenas and 
