§ 233. The radially-symmetrical form is common to all individual flowers that have vertical axes. In plants which are practically if not literally uniaxial, and bear their flowers at the ends of upright stalks, so that the faces open horizontally, the petals are disposed in an all-sided way. Crocuses, Tulips, and Poppies are familiar examples of this structure occurring under these conditions. A Ranunculus flower, Fig. 228, will serve as a typical one. Similarly, flowers which have peduncles flexible enough to let them hang directly downwards, and are not laterally incommoded, are also radial; as in the _Fuchsia_, Fig. 229, as in _Cyclamen_, _Hyacinth_, &c. These relations of form to position are, I believe, uniform. Though some flowers carried at the ends of upright or downright stems have oblique shapes, it is only when they have inclined axes or are not equally conditioned all round. No solitary flower having an axis habitually vertical, presents a bilateral form. This is as we should expect; since flowers which open out their faces horizontally, whether facing upwards or downwards, are, on the average, similarly affected on all sides. [Illustration: Figs. 228, 229.] [Illustration: Figs. 230, 231.] At first it seems that flowers thus placed should alone be radial; but further consideration discloses conditions under which this type of symmetry may exist in flowers otherwise placed. Remembering that the radial form is the primitive form--that, morphologically speaking, it results from the contraction into a whorl, of parts that are originally arranged in the same spiral succession as the leaves; we must expect it to continue wherever there are no forces tending to change it. What now must be the forces tending to change it? They must be forces which do not simply affect differently the different parts of an individual flower. They must be forces which affect in like contrasted ways the homologous parts of other individual flowers, both on the same plant and on surrounding plants of the same species. A permanent modification can be expected only in cases where, by inheritance, the effects of the modifying causes accumulate. That they may accumulate the flowers must keep themselves so related to the environment, that the homologous parts may, generation after generation, be subjected to like differentiating forces. Hence, among a plant’s flowers which maintain no uniformity in the relations of their parts to surrounding influences, the radial form will continue. Let us glance at the several causes which entail this variability. When flowers are borne on many branches, which have all inclinations from the vertical to the horizontal--as are the flowers of the Apple, the Plum, the Hawthorn--they are placed in countless different attitudes. Consequently, any spontaneous variation in shape which might be advantageous were the attitude constant, is not likely to be advantageous; and any functionally-produced modification in one