It is so necessary to appreciate the important effects of the laws of
growth, that I will give some additional cases of another kind, namely of
differences in the same part or organ, due to differences in relative
position on the same plant. In the Spanish chestnut, and in certain fir-
trees, the angles of divergence of the leaves differ, according to Schacht,
in the nearly horizontal and in the upright branches. In the common rue
and some other plants, one flower, usually the central or terminal one,
opens first, and has five sepals and petals, and five divisions to the
ovarium; while all the other flowers on the plant are tetramerous. In the
British Adoxa the uppermost flower generally has two calyx-lobes with the
other organs tetramerous, while the surrounding flowers generally have
three calyx-lobes with the other organs pentamerous. In many Compositae
and Umbelliferae (and in some other plants) the circumferential flowers
have their corollas much more developed than those of the centre; and this
seems often connected with the abortion of the reproductive organs. It is
a more curious fact, previously referred to, that the achenes or seeds of
the circumference and centre sometimes differ greatly in form, colour and
other characters. In Carthamus and some other Compositae the central
achenes alone are furnished with a pappus; and in Hyoseris the same head
yields achenes of three different forms.
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