. The classification of flowering plants. Plants. LEGUMINOSAE 355 and two alternating rows of ovules on the ventral suture of the ovary which faces the back of the flower. The arrangement and form of the perianth-segments, especially of the corolla, and the number and cohesion of the stamens, shew considerable variation. Three well-marked types are recognised, each characteristic of a subfamily. In Mimosoideae, the smallest subfamily with about 40 genera, the flower is regular and the aestivation of both calyx and corolla valvate; Parkia and an allied genus have imbricate sepals; (fig. 175). T
. The classification of flowering plants. Plants. LEGUMINOSAE 355 and two alternating rows of ovules on the ventral suture of the ovary which faces the back of the flower. The arrangement and form of the perianth-segments, especially of the corolla, and the number and cohesion of the stamens, shew considerable variation. Three well-marked types are recognised, each characteristic of a subfamily. In Mimosoideae, the smallest subfamily with about 40 genera, the flower is regular and the aestivation of both calyx and corolla valvate; Parkia and an allied genus have imbricate sepals; (fig. 175). The perianth is generally penta- merouSjbut 3-, 4- or 6-merous flowers occur: Mimosapudica is tetramerous, and all four forms are found in the genus Mimosa; while in Acacia many species are 3- or 4-merous. The sepals are more or less united below into a cup, and the petals may also cohere at the base. The stamens vary greatly in number; their number and cohesion afford distinctive tribal characters. Thus they are indefinite and free in Acacieae (containing the single large genus Acacia) (figs. 175, C, 176), indefinite and more or less monadelphous in Ingeae. In the four other tribes they are as many or twice as many as the petals. The long slender filaments are* crow^ned by small bilocular anthers which dehisce longitudinally. The pollen-grains are often united into little packets. Occasionally the anther- chambers are divided by several transverse septa. In many cases the long exserted yellow stamens are, as in Mimosa, the most conspicuous part of the flower. In Caesalpinioideae (133 genera) the flowers are medianly zygomorphic, and generally 5-, more rarely 4-merous. The two upper sepals are sometimes united, as in Tamarindus (fig. 179, B), othermse the members of the calyx are generally free; their aestivation is imbricate, rarely, as in Cercis Siliquastrum (Judas-tree) (fig. 179, A), valvate. The typically pentamerous corolla shews great variation. Its aestivation is ascendi
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