Evolution of sex in plants / by John Merle Coulter.

  • Coulter John Merle, 1851-1928.
Date:
[1914]
Catalogue details

Licence: In copyright

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

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    61/160 (page 47)
    led to so rigid a definition of a sperm that if the sperm generation was omitted it was concluded that there were no sperms. For example, this is just what happens in the spermatogenesis of all angiosperms and many g) mnosperms. The cell generations succeed one another until the mother-cell appears, but it does not organize and discharge a sperm. The usual formula for describ- ing this situation has been to say that “the mother-cell functions directly as a sperm,” implying that in fact there is no sperm, but that the mother-cell behaves like one. Since the test of a gamete through all its history has been its behavior, it is difficult to understand such a statement except that a secondaiv’ feature has been substituted for the essential one. Moreover, the situ- ation is ex])lained easily on the basis of what has been observed in connection with spore-formation. Under certain conditions, it will be remembered, ])rotoplasts separate from their walls and are discharged as spores, thus securing the opportunity to produce new indi- viduals rather than to contribute merely to the growth of a single individual. In the same way protoplasts separate from their walls and are discharged as swimming sperms. It is obvious that if organization by a mother- cell and discharge of a sperm are essential to secure freedom of ajiproach to the egg, when another method of aj)proach is secured the necessity for discharge will disappear. The protoj)last within the mother-cell and the discharged sperm are the same protoplast, and the mother-cell of angiosperms behaves like a sperm, therefore, because it is a sperm; one without swimming apparatus or organization of any kind that differs in appearance from the protoplast of an ordinar\' cell.