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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    without fusing. Finally, at some i^eriod in the life his- tory' their fusion occurs, and this is followed by cell generations which are uninucleate. If this fusion represents the sex act, the gametic nuclei are long in proximity before they develo]) the mutual attraction that leads to contact and fusion. It might be regarded as the last stage before the complete elimination of sex. The special features of the sex organs of Charales and red algae, and the apparent reduction of sex organs among fungi, do not represent the general evolution of sex organs. 'Fhey are special lines of evolution in response to special conditions. The general line of evolution proceeded from the simple oogonia and antheridia of the ordinar>’ algae to the sex organs of liverworts, which may be regarded as representing the second stage in the general evolution of sex organs, d'he conditions that determine this transition must be considered. It is generally conceded that the transition from the green algae to the liverworts was associated with the acquisition of the land habit by plants. The algae are essentially water j)lants, and all their structures and habits are to be explained by that fact. As certain of the green algae acquired the ability to endure aerial conditions, they became so changed in structure that they constituted the most primitive land group, the liverworts. The appearance of liverworts was one of the most important epochs in the history of ])lants, for it was the beginning of a land flora, which led on to the higher groups of plants. The total structure of a simple liverwort can be explained as a response to aerial con-