being prevented from producing sexual individuals by excessive nutrition, plants are, by excessive nutrition, made to change the sexual individuals they were about to produce, into sexless ones. This arrest of gamogenesis may be seen in various stages. The familiar instance of flowers made barren by the transformation of their stamens into petals, shows us the lowest degree of this reversed metamorphosis. Where the petals and stamens are partially changed into green leaves, the return towards the agamogenetic structure is more marked; and it is still more marked when, as occasionally happens in luxuriantly-growing plants, new flowering axes, and even leaf-bearing axes, grow out of the centres of flowers.[31] The anatomical structure of the sexual axis affords corroborative evidence: giving the impression, as it does, of an aborted sexless axis. Besides lacking those internodes which the leaf-bearing axis commonly possesses, the flowering axis differs by the absence of rudimentary lateral axes. In a leaf-bearing shoot the axil of every leaf usually contains a small bud, which may or may not develop into a lateral shoot; but though the petals of a flower are homologous with leaves, they do not bear homologous buds at their bases. Ordinarily, too, the foliar appendages of sexual axes are much smaller than those of sexless ones--the stamens and pistils especially, which are the last formed, being extremely dwarfed; and it may be that the absence of chlorophyll from the parts of fructification is a fact of like meaning. Moreover, the formation of the seed-vessel appears to be a direct consequence of arrested nutrition. If a gloved-finger be taken to represent a growing shoot, (the finger standing for the pith of the shoot and the glove for the peripheral layers of meristem and young tissue, in which the process of growth takes place); and if it be supposed that there is a diminished supply of material for growth; then, it seems a fair inference that growth will first cease at the apex of the axis, represented by the end of the glove-finger; and supposing growth to continue in those parts of the peripheral layers of young tissue that are nearer to the supply of nutriment, their further longitudinal extension will lead to the formation of a cavity at the extremity of the shoot, like that which results in a glove-finger when the finger is partially withdrawn and the glove sticks to its end. Whence it seems, both that this introversion of the apical meristem may be considered as due to failing nutrition, and that the ovules growing from its introverted surface (which would have been its outer surface but for the defective nutrition) are extremely aborted homologues of external appendages: both they and the pollen-grains being either morphologically or literally quite terminal, and the last showing by their dehiscence the exhaustion of the organizing power.[32]