Page:Natural History Review (1861).djvu/466

454 since appeared separately, is of enormous length, occupying about 150 quarto pages. Only a small portion of it, however, relates directly to the simple question of the existence, or non-existence, of fructification without impregnation. The author expressly contradicts the theory advanced by Klotzsch as to the nature of the body within the seeds of Cœlebogyne. He says: "I can confidently reaffirm, and prove at any time by sections of seeds in my possession, that the embryo-formation of Cœlebogyne which I have observed and described, fulfils all the conditions necessary to constitute a veritable embryo, and agrees in its essential features with that of the other Euphorbiaceæ." In a later part of the essay some remarks are given under the head "Weitere Zeugnisse für die Parthenogenesis," of which the following is a short account. Some observations on individual plants given by Ruprecht, Tenore, Lecoq, and Jacquemont are noticed, the author stating that he was un- willing to pass them over entirely, although (he adds), as merely special instances, little importance may be attached to them. Dr. Braun then refers (as bearing upon the question of parthenogenesis) to those cases of fructification called by Gartner Fructifcatio spuria, in which fruit is formed, and even seeds also; the latter being apparently perfect, but containing no embryo. Instances of this occur in Datisca, Adelia, the Cycadeæ, and the Conifers; and give rise to the question, whether the unimpregnated germinal vesicle disappears without undergoing any development; or whether the development progresses to a certain extent, and is then arrested. Dr. Braun considers this point deserving of investigation, as, in his opinion, it is not improbable that, besides perfect parthenogenesis, there may exist indications of parthenogenesis, as has been observed in the animal kingdom. The above question, he adds, is connected with the further ones; 1, whether or not, speaking generally, the formation of seeds and fruits depends upon the development of the germinal vesicle into an embryo; and, 2, whether, when impregnation occurs, it acts directly only upon the development of the germinal vesicle into an embryo, and thus indirectly upon the formation of the surrounding parts; or whether impregnation acts upon the entire ovule, or even upon the ovary itself. Observations, he says, are wanting as to the well-known cases of fructification without seeds which occurs in certain cultivated varieties of Citrus, Pyrus, Cydonia, Vitis, Arlocarpus, Musa, and Ananassa. It should be ascertained in what stage of development the ovules fail, and whether the formation of these seedless fruits is in all cases independent of impregnation.

Having regard to the cases in which parthenogenesis has been noticed in the animal kingdom, Dr. Braun observes that it might be expected to play a more important part amongst cryptogamic, than amongst phænogamic plants. He adds, however, that this question is surrounded by many difficulties, and that he can do no more than make a few suggestions on the subject. He alludes, in the first place, to the ferns, in which he considers that the constant reappearance