The evolution of sex in plants / by John Merle Coulter.

  • John Merle Coulter
Date:
[1914]
Catalogue details

Licence: In copyright

Credit: The evolution of sex in plants / by John Merle Coulter. Source: Wellcome Collection.

    148/160 (page 134)
    If gametes were, the only cells that pair and fuse, no further explanation of sexuality would seem necessary, but, with other cell fusions occurring, a distinction must be made. In many cell fusions the cytoplasms only are involved, the nuclei remaining distinct. Since it is well established that sexual fusion is essentially a fusion of nuclei, such cases do not obscure the problem. There are many cases of nuclear fusion, however, which do not appear to be sexual fusion, and these obscure the prob- lem seriously. It is entirely possible that all nuclear fusions represent sexual fusions whose results are obscured in some way. This would be the easiest way of disposing of the difficulty, for in this case any pairing cells resulting in nuclear fusion would represent sexual cells, and these could be differentiated from all other cells by containing the mutually attractive substances. But such an escape from the difficulty is hardly justi- fiable, and a further explanation is necessary. The nuclear fusion referred to as occurring in the angiosperm embryo sac, in which a sperm fuses with cells that are not eggs, is regarded by many as a real sexual fusion. In fact, the occurrence of the two fusions of sperms in the embryo sac, one with the egg and the other with the endosperm nucleus, is usually called “double fertilization.” This case may be waived as still within the region of discussion, but certainly the result of this debated nuclear fusion is not at all the result that follows the sex act. The nuclear fusion that occurs in connection with spore-formation in the Ascomy- cetes has been regarded as a sexual fusion, but, if so. there would be two separate sex acts in the life histories of certain Ascomycetes, which would introduce us to a