§ 197. And now it remains only to observe, in confirmation of the foregoing synthesis, that it at once explains for us various irregularities. When we see leaves sometimes producing leaflets from their edges or extremities, we recognize in the anomaly a resumption of an original mode of growth: fronds frequently do this. When we learn that a flowering plant, as the _Drosera intermedia_, has been known to develop a young plant from the surface of one of its leaves, we are at once reminded of the proliferous growths and fructifying organs in the Liverworts. The occasional production of bulbils by Phænogams, ceases to be so surprising when we find it to be habitual among the inferior Acrogens, and when we see that it is but a repetition, on a higher stage, of that self-detachment which is common among proliferously-produced fronds. Nor are we any longer without a solution of that transformation of foliar organs into axial organs, which not uncommonly takes place. How this last irregularity of development is to be accounted for, we will here pause a moment to consider. Let us first glance at our data. The form of every organism, we have seen, must depend on the structures of its physiological [or constitutional] units. Any group of such units will tend to arrange itself into the complete organism, if uncontrolled and placed in fit conditions. Hence the development of fertilized germs; and hence the development of those self-detached cells which characterize some plants. Conversely, physiological units which form a small group involved in a larger group, and are subject to all the forces of the larger group, will become subordinate in their structural arrangements to the larger group--will be co-ordinated into a part of the major whole, instead of co-ordinating themselves into a minor whole. This antithesis will be clearly understood on remembering how, on the one hand, a small detached part of a hydra soon moulds itself into the shape of an entire hydra; and how, on the other hand, the cellular mass that buds out in place of a lobster’s lost claw, gradually assumes the form of a claw--has its parts so moulded as to complete the structure of the organism: a result which we cannot but ascribe to the forces which the rest of the organism exerts upon it. Consequently, among plants, we may expect that whether any portion of protoplasm moulds itself into the typical form around an axis of its own, or is moulded into a part subordinate to another axis, will depend on the relative mass of its physiological units--the accumulation of them that has taken place before the assumption of any structural arrangement. A few illustrations will make clear the validity of this inference. In the compound leaf, Fig. 65, the several lateral growths _a_, _b_, _c_, _d_, are manifestly homologous; and on comparing a number of such leaves together, it will be seen that one of these lateral growths may assume any degree of complexity, according to the