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.

    130/160 (page 116)
    (zygote), which has certainly received both sex- determiners, ])roduces either a megasporangiate sporo- ])hytc (one with pistillate dowers) or a microsporangiate sporophyte (one with staminate flowers), d'here is no apparent difference in the eggs to account for these ver>' (lifTerent results, d'he pistillate plant produced by the egg matures megaspores, which in germination produce female gametophytes; while the staminate plant pro- duced by an egg of apparently the same constitution matures microspores, which in germination produce mal6 gametophytes. 'Fhe temptation is to imagine that in the germination of the egg, either only one kind of determiner is passed on, or, in passing both on, they are accompanied by an inhibitor for one of them. The occasional departure from the strictly dioecious habit here suggests the latter alternative. An additional complexity is involved in the case of the dioecious seed plants. If a pistillate sporophyte contains only female determiners, or an inhibitor for the male determiners, this results not merely in the production of megaspores, but also in the development of all the structures related to megaspores, namely, jnstils and pistillate flowers. In other words, the se.x- determiner, being transmitted through the sporo])hyte to ex])ress itself later in the gametophyte, determines in the mean time the character of the flower. After tracing the origin and history of sexual indi- viduals among plants by means of the illustrations given above, taken to represent clifTerent situations and different plant levels, the complexity of the problem is apparent, but the facts ])oint to certain tentative conclusions.