As to another phase in this question, there are, as Krempelhuber remarks, species of lichens which in many countries do not fructify, and whose propagation can only be carried on by means of the soredia, and the hyphæ of such could in themselves alone no more serve for propagation than the hyphæ from the pileus or stalk of an Agaric, while it is highly improbable that they could acquire this faculty by interposition of a foreign algal. On the other hand he argues: "It is much more conformable to nature that the gonidia, as self-developed organs of the lichens, should, like the spores, enable the hyphæ proceeding from them to propagate the individual."[O] A case in point has been adduced[P] in which gonidia were produced by the hypha, and the genus _Emericella_,[Q] which is allied to _Husseia_ in the _Trichogastres_, shows a structure in the stem exactly resembling _Palmella botryoides_ of Greville, and to what occurs in _Synalyssa_. _Emericella_, with one or two other genera, must, however, be considered as connecting _Trichogastres_ with lichens, and the question cannot be considered as satisfactorily decided till a series of experiments has been made on the germination of lichen spores and their relation to free algæ considered identical with gonidia. Mr. Thwaites was the first to point out[R] the relation of the gonidia in the different sections of lichens to different types of supposed algæ. The question cannot be settled by mere _à priori_ notions. It is, perhaps, worthy of remark that in _Chionyphe Carteri_ the threads grow over the cysts exactly as the hypha of lichens is represented as growing over the gonidia. Recently, Dr. Thwaites has communicated his views on one phase of this controversy,[S] which will serve to illustrate the question as seen from the mycological side. As is well known, this writer has had considerable experience in the study of the anatomy and physiology of all the lower cryptogamia, and any suggestion of his on such a subject will at least commend itself to a patient consideration.