comparatively marked and constant proximity in _B. pruinata_, Fig. 224, we see a more decidedly unsymmetrical shape; and in _B. mahringii_, Fig. 225, the modification thus caused is pushed so far as to destroy the peltate structure.[34] [Illustration: Figs. 222–225.] § 231. Again, then, we are taught the same truth. Here, as before, we see that homologous units of any order become differentiated in proportion as their relations to incident forces become different. And here, as before, we see that in each unit, considered by itself, the differences of dimension are greatest in those directions in which the parts are most differently conditioned; while there are no differences between the dimensions of the parts that are not differently conditioned.[35] CHAPTER X. THE SHAPES OF FLOWERS. § 232. Following an order like that of preceding chapters, let us first note a few typical facts respecting the forms of clusters of flowers, apart from the forms of the flowers themselves. Two kindred kinds of _Leguminosæ_ serve to show how the members of clusters are distributed in an all-sided manner or in a two-sided manner, according as the circumstances are alike on all sides or alike on only two sides. In _Hippocrepis_, represented in Fig. 226, the flowers growing at the end of a vertical stem, are arranged round it in radial symmetry. Contrariwise in _Melilotus_, Fig. 227, where the axillary stem bearing the flowers is so placed in relation to the main stem, that its outer and inner faces are differently conditioned, the flowers are all on the outer face: the cluster is bilaterally symmetrical, since it may be cut into approximately equal and similar groups by a vertical plane passing through the main axis. [Illustration: Figs. 226, 227.] Plants of this same tribe furnish clusters of intermediate characters having intermediate conditions. Among these, as among the clusters which other types present, may be found some in which conformity to the general law is not obvious. The discussion of these apparent anomalies would carry us too much out of our course. A clue to the explanation of them will, I believe, be found in the explanation presently to be given of certain kindred anomalies in the forms of individual flowers.