The leaves of the true mosses and those of the club-mosses (Lycopodium, Selaginella) being somewhat alike in general appearance and in ontogeny, might be, and indeed have been, regarded as homologous on that ground.
He was an enthusiast for evolution and saw in the growth of embryos what he called ' ontogeny recapitulates phylogeny ' .
The most striking general change has been against seeing in the facts of ontogeny any direct evidence as to phylogeny.
The term morphology, which was introduced into science by Goethe (1817), designates, in the first place, the study of the form and composition of the body and of the parts of which the body may consist; secondly, the relations of the parts of the same body; thirdly, the comparison of the bodies or parts of the bodies of plants of different kinds; fourthly, the study of the development of the body and of its parts (ontogeny); fifthly, the investigation of the historical origin and descent of the body and its parts (phylogeny); and, lastly, the consideration of the relation of the parts of the body to their various functions, a study that is known as organography.
It was formerly assumed, and the view is still held, that the foliage-leaf was the primitive form from which all others were derived, mainly on the ground that, in ontogeny, the foliage-leaf generally precedes the sporophyll.