in _Selaginella_ and _Isoëtes_, which have the two kinds of sporangia borne on _different_ leaves. The division of labour (modification) is, however, still more pronounced in the _Phanerogams_: the leaves which bear the microsporangia (“pollen-sacs”) have quite different forms from those which bear macrosporangia (the “nucellus” in the ovule), the former are termed _stamens_, the latter _carpels_; in certain instances, too, there is even a contrast between the “male plants” and the “female plants.” Moreover, a division of labour, in a much greater degree, takes place in the leaves which do not directly take part in reproduction, and it is thus possible in many plants to draw a sharp line not only between stamens and carpels, but also between four or five distinct kinds of leaves, which differ in _form_, _structure_, and corresponding _functions_, and which appear in regular sequence on the shoot: namely, between “scale-leaves” and “foliage-leaves,”[21] both of which occur in the Cryptogams, and the “floral-leaves,” including the bracts and leaves of the “perianth,” which latter often differ from each other in form and colour, and are then separated into _sepals_ and _petals_. The _leaves_--stamens and carpels--_which bear the sporangia_ are termed sporophylls, and the shoot, or extremity of a shoot, whose leaves are modified into sporophylls, is _terminated in its further growth by their production, and is known as a flower_. The flower which is most completely furnished has calyx, corolla, stamens, and carpels arranged in this order. If the only sporophylls present are stamens, then it is said to be a _male_ (_staminate_) flower, and if only carpels, then a _female_ (_pistillate_) flower, and in both these cases the flowers are _unisexual_, or diclinous. If stamens and carpels are both present in the same flower, it is termed _hermaphrodite_. Diclinous plants in which the female flowers are situated on one plant, and the male flowers on another, are termed _diœcious_; and those in which the same plant bears the two kinds of flowers are termed _monœcious_. When the male, female, and hermaphrodite flowers are found in the same species, the plant is said to be _polygamous_.