/ ¢ n oa | ¥ - —— 
“ : \y 7 , F : ; PAT 
- . . - 
: i T. he External Form of Plants. ca 13 
- polygamous. Examples of moncecious. plants occur in the 
oak, walnut, birch, and Caditriche ; of dicecious plants in the 
juniper and poplar; of polygamous in the maple, eim, and 
horse-chestnut. 
The centre of a perfect flower is occupied by the pistil, 
around which are grouped first the stamens, next the corolla, 
and finally the calyx, arranged in whorls or spiral lines. 
The greatest diversity, however, prevails in the mutual posi- 
tion of the individual organs, which is best recognised by a 
longitudinal section of the flower, and by the floral diagram 
or cross section. In Fig. 204, for example, which represents 
: sna! lite 
- iS 
Fic. 205.—Diagram of the flower Fic. 206.—Diagram of the flower of Ranun- 
of Khamnus Frangula; with culus acris; with five imbricate sepals, five 
five valvate sepals, five folded imbricate petals alternate with the sepals (both 
_ petals, five stamens opposite the quincuncial),a very large number ot stamens, 
petals, and a trilocular cvary. © and a large number of distinct carpels. 
diagrammatically the cross, section of a cruciferous flower, it 
is seen that the calyx, K, consists of two whorls, each of two 
leaves, with alternate zestivation; the corolla, B, of one whorl 
of four leaves with valvate zestivation ; while the andrecium, 
s, also consists of two whorls, the outer one of two, the inner 
one of four stamens. ‘lhe leaves of the corolla alternate 
with those of the calyx ; the stamens of the inner whorl stand 
in front of (in other words, are opposite to or superposed- 
upon) the leaves of the corolla, the two outer ones being 
I 
