The integuments of the ovule become the seed coats.
The stamens have their position next below the pistils on the torus. Technically a stamen is a microsporophyll and consists of a stalk (filament) and an enlarged extremity (anther). The anther consists of a usually narrow portion (connective) bearing on each side two microsporangia or pollen sacs. Within these are produced the microspores or pollen, consisting of round or angular, sometimes elongated, usually yellow or orange, less often green cells. These are smooth or marked in characteristic patterns by ridges, spines, pits, etc. They escape by the rupture of the pollen sacs by a longitudinal split or by the opening of little lids, usually at the apex. The pollen may be dry and dust-like and adapted to distri bution by the wind or sticky and occurring more or less in masses, depending upon insects, in the main, for distribution. The stamens may be very numerous and arranged spirally on the torus or few in number, forming one or two whorls.
Next to the stamens are the petals (collec tively the corolla). These are more or less leaf like, thin, mostly white or brightly colored struc tures, less often green or dull in color. They may be numerous and spirally attached to the torus or in a single Whorl of but a few petals. In some flowers they are entirely lacking (apetaly). The petals of a flower may be united to each other to form a gamopetalous corolla.
The outermost members of the flower are the sepals (collectively the calyx). They are usu ally green and more leaf-like than the petals and form the outer layer of the flower bud, enclosing the other parts. They may be numer ous and spirally arranged or few and in a whorl. In the absence of the petals the sepals of some kinds of .flowers are brightly colored, as in the anemone, four-o-clock, buckwheat, etc. Like the petals the sepals may be separate or united.
In some flowers the calyx also is lacking, in which case the flower is called naked or achla mydeous.
The torus may he more or less elon gated, so that the pistil or pistils, stamens,petals and sepals follow one another downward, e.g., buttercup or magnolia, or flattened so that the pistil is in the centre with the other organs successively further from the centre, e.g., pink,
or it may be saucer- or cup-shaped bearing the pistil or pistils in the centre and the stamens, petals and sepals on the rim of the cup, e.g., plum and rose. Flowers of the last type are called perigynous and of the first two hypogy nous. A still further modification is that where the hollowed out torus is grown fast to the enclosed pistil so that the remaining organs of the flower appear to arise from the top of the ovary (epigynous flower), e.g., apple, evening primrose, etc.
Variations in Structure and Arrangement. — In general the flowers of the Monocoty ledonew have their parts in threes, those of the Dicotyledonem in fives or fours, with numerous exceptions in both groups. Probably the majority of the former group possess pentacy clic flowers, i.e., with five whorls, sepals, petals, stamens (two whorls) and carpels (usually united into a compound pistil). The members of each whorl alternate in position with those of the next whorl, so that the petals stand op posite the stamens of the inner whorl and alter nate with those of the outer whorl as well as with the sepals. Since the number three pre vails largely throughout this class it is apparent that where but two or only one member is present the others have been lost in some way, leaving a gap. In the Dicotyledoneir many flowers are spiral in their arrangement, others have their sepals and petals in alternating whorls of five each with numerous stamens and pistils; the most, however, possess a penta cyclic or even more frequently a tetracyclic type of flower. In the latter case it is usually the inner whorl of stamens that is missing; in the Primroses, however, the outer whorl. There is also a great tendency toward the reduction of the carpellary whorl to three or even two carpels, the other whorls remaining in fives. It is true that in the Mintk and Foxgloves (respectively Lamiacece and Scrophulariacce) we frequently find but four or even two stamens while the petals and sepals remain in fives. In these cases we can see the gaps left by the miss ing stamens and reconstruct it as an incomplete whorl of five. In these same flowers the carpels are but two.