190 EVOLUTION OF PLANTS 
fests itself first in the development of a colored peri- 
anth or floral envelope, hence they are known as the 
“petaloideous” Monocotyledons. Most of these have 
the carpels more or less perfectly grown together into 
a compound pistil. ~° 
In the great majority of the petaloideous forms the 
parts of the flower are in whorls of three, the typical 
arrangement being shown in the accompanying dia- 
gram (Fig. 46, D). The two sets of leaves constituting 
the perianth are usually alike in color and texture, but 
occasionally, e.g. Trillium, the outer leaves are green, 
and form a calyx like that found in most Dicotyledons. 
The six stamens are in two alternating whorls, and the 
three carpels completely coherent. 
Probably the lowest of the petaloideous series with 
coherent carpels are the lilies, with their regular flowers 
showing perfect radial symmetry. Here are found 
many of the most magnificent of all flowers, and the 
brilliant colors and fragrance of many of them show 
their adaptation to insect aid in their pollination. 
Starting from the type exhibited by the simpler mem- 
bers of the lily family, it is easy to see how specializa- 
tion has progressed in different directions. This is first 
seen in the coherence of the leaves of the perianth, so 
that the flower becomes tubular, as in the hyacinth or 
tuberose. This is sometimes accompanied by a slight 
inequality in the size of the perianth lobes, especially 
if the flower is nodding, and in such cases the stamens 
and pistil are declined so that the flower is more or less 
markedly two-lipped (Fig. 46, H). Carried further, the 
cohesion of the perianth extends to the pistil, and the 
result is a tubular flower with a so-called “inferior” 
