DIVERSITY OF FLOWERS. In the most primi tive flowers the parts have a spiral arrange ment. For example. the sepals, petals, and stamens are not in definite rosettes or cycles, but appear at different levels and may be in definitely repeated. In this case there is no such thing as definite numbers. In the more highly developed flowers, however, the spiral arrange ment passes into the cyclic, in which the members of each set form a definite rosette or cycle. in which the numbers are limited. Usually these numbers are definite for great groups, the pre vailing, number in the cyclic monocotyledons be ing three and the prevailing number in the cyclic dicotyledons being five or four. One of the com mon causes of diversity among flowers is the ab sence of one or more of the four sets, or of some member or members in a single set. This may he the primitive condition of the flower, in which the given set or member is not to be expected: or it may be a ease of abortion or suppression, which means that organs which are to be expected have failed to develop, although they may do so par tially. As prominent illustrations of such diver sities the following may he mentioned. It fre quently happens that but a single set of floral leaves appears, and it is customary to regard the missing set as the petals, such flowers being called `apetalons.' In other cases neither calyx nor corolla appears, in which ease the flower is said to be 'naked.' In still other eases the stamens: are lacking, and if a pistil be present the flower is said to be `pistillate.' If the pistil is lacking and the stamens arc present. the flower is `staminate ;' while if both stamens and pistils are lacking, the flowers are 'neutral.' Other diversities arise from the fact that the members of a set may to great er or lesser degree lose their independence and develop in common, giving the appearance of coalescence. For ex ample. the sepals may organize an urn-shaped or tubular calyx. or the petals may organize a co rolla which resembles a 1nhe, a funnel. a hell, etc. The terminology used in such eaSes, implies that members originally separate have coalesced; but the fact is that there has been no coalescence of distinct parts, lout a ringlike outgrowth instead of growth at separate points. Flowers with a corolla
of this kind are said to be 'sympetalous' petalous,"gainopetalous'). The same tendency is shown by the stamen set; while it is exceedingly common among the carpels, in which latter case the flower is said to be •synearpous,' resulting in the so-called 'compound pistil.' The sympetalous character of flowers is so definitely associated with natural groups that the character gives name to the great group Sympetahr. which is one of the two large divisions oI dicotyledons. The con trasting condition of flowers, namely, the occur rence of petals entirely distinct from one another, is called 'polyfletalous,' such flowers being re garded as more primitive than sympetalous flowers.
Another source of diversity in flowers is the tendency of contiguous sets to become more in timately related than usual. For example, the stamens and petals may be so intimately re lated to one another in origin that the former seem to arise from the latter. This condition is common in sympetalous flowers, where the stamens are said to be 'inserted upon the tube of the corolla.' This apparent coalescence of ad jacent sets is frequently called 'adhesion,' a term which implies that the two sets are normally dis tinct, but have become adherent. Such an ex planation is no more true than that which was given to the apparent coalescence of the members of a single set. This tendency of different sets to arise together, rather than separately. has re sulted in three well-marked conditions. When the sepals, petals, and stamens all rise from be neath the ovary, the flower is said to be 'hypo ulna's,' or to have a 'superior ovary.' Ilis is the most primitive condition. When these three outer parts arise from the rim of an urn-like outgrowth from the receptacle ('torus'), which surrounds the pistil or pistils, the flower is said to be 'perigynous; Finally, the insertion of the outer parts may be carried above the ovary, from the sununit of which the sepals, petals, and sta mens seem to arise, such a flower being called `epig,ynous,' or said to have an 'inferior ovary.'