The second cause by which the symmetry may be obliterated, namely degeneration, asserts itself in the formation of thorns, of threadlike prolongations of membranous expansions, and in the production of fleshy parts, or of parts with dry membranes. The third kind of departure from the symmetrical plan is the adherence of parts, the theory of which he grounds first and chiefly on the phenomena of grafting, and then passes to more difficult cases. The close packing of the ovaries in some species of honeysuckle, is, he says, the primary cause of their adherence. This therefore does not depend on the plan of symmetry, but upon an accident, which however is constant in its appearance, owing to the specific constitution of such plants. In connection with the phenomena of adherence he next considers the question whether a structure composed of several parts, as for instance a compound ovary, should be considered as originally simple and afterwards divided into parts, or whether the converse is the true account, and he says that we must examine each particular case and decide which is the correct conception. Thus it may be shown that the perfoliate leaves of honeysuckles, as well as the involucres of many Umbelliferae, and monosepalous calyces and monopetalous corollas are due to adherence, and he proceeds to prove that ovaries with several loculaments and several parts have in like manner been formed by adherence of two or more carpellary leaves, and concludes by pointing out the systematic importance of such considerations. Further on he takes occasion to speak of the significance of the relative number of the parts of the flower, on which head he says much that is good, but does not thoroughly investigate the matter; it was not till a later time that Schimper’s doctrine of phyllotaxis made it possible to express these relations of number and position more precisely.