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.

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    CHAPTER IV THE EVOLUTION OF SEX OROANS When gametes first appeared among the algae as modified swimming s])ores, they were produced by the protoplasts of ordinary vegetative cells, which under dilTerent conditions functioned vegetatively, divided to form spores, or divided to form gametes. The first dilTerentiation was the production of special gamete- producing cells {gamclangia). This seems to have preceded the dilTerentiation of spore-producing cells {spo- rangia), and the reason appears obvious. The conditions favoring gamete-production are much more differen- tiated from those favoring vegetative activity than arc those favoring spore-formation. The production of gametes belongs to the end of seasonal activity, and thus the function of the cells producing them is dis- tinctly set apart in time from the function of ordinary cells. In many cases ordinary vegetative cells, functioning later in the season as gametangia, become transformed in appearance, so that they arc as dilTerent in appearance from ordinary cells as they are in function (Fig. i8). This may be regarded as an intermediate stage between gametangia which are unchanged vegetative cells, and those which are never vegetative cells. The three stages in the differentiation of a sex organ, therefore, are: (i) a vegetative cell changed in function; (2) a vegetative cell changed in form as well as in function; (3) a cell which is never a vegetative cell.