206 EVOLUTION OF PLANTS 
of the flower as well; but in a larger number the carpels 
are more or less completely coherent, and the sepals are 
also frequently united into a cup-shaped or tubular calyx. 
The lowest of the Choripetale are the Amentacez, so 
named from usually having the simple flowers in elon- 
gated catkins or aments. The willows (Fig. 49, A-D), 
poplars, and various nut-trees are familiar examples of 
this group. A second order allied to these includes the 
Fic. 49 (Lower Dicotyledons— Amentacexz, Centrosperme).— A, male 
inflorescence of a willow; B, an individual staminate flower consist- 
ing of two stamens surrounded by inconspicuous bracts; C, a female 
inflorescence of a willow, each flower (D) consisting of a single pistil 
made up of two coherent carpels; E, flower of a knot-grass (Polygo- 
num); the perianth consists of five colored sepals; F, the pistil of E, 
with the side of the ovary cut away to show the single ovule borne at 
the apex of the floral axis; G, section of the flower of a scarlet catchtly 
(Silene) ; the sepals are united into a tube enclosing the free petals and 
stamens; the petals are showy, and the flower is pollinated by insects; 
H, diagram of the flower of Silene; the pistil is composed of three 
carpels; the central axial placenta bears numerous ovules. 
& 
pepper family, a tropical group which superficially, at 
least, shows a curious similarity to the aroids, and may 
prove to comprise connecting forms between Mono- 
cotyledons and Dicotyledons. In these low types the 
flowers are often diclinous, ¢.e. stamens and carpels are 
in separate flowers and no perianth is present, or the 
perianth is reduced to inconspicuous scales. It is gen- 
erally supposed that these amentaceous Dicotyledons 
