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 III THE DIFFERENTIATION OF SEX The differentiation of sex to be discussed may be called in general moqjhological differentiation. In the preceding chapter attention was called to the fact that two pairing gametes, although alike in appearance, must be different physiologically. By morphological differ- entiation is meant difference in appearance, and there- fore a visible difference. In the case of gametes, this visible difference involves size and activity, with such motile organs as may go with activity. In this sense, therefore, the differentiation of sex means such a differ- entiation of gametes that they can be recognized as male and female. Of course morphological dilTer- entiation must have been brought about by physio- logical differentiation, and the physiological changes, of which the morphological changes are but an index, must have been very great. Morphological likeness of pairing gametes, as stated in the preceding chapter, is called isogamy, while moq)hological unlikeness of pairing gametes is called helerogamy. In isogamous plants, therefore, the terms “male” and “female” are not used, but in heterogamous plants they become current. The t>pe of gamete that gradually gave rise to dis- similar gametes was clearly the active swimming-spore ty])e, the two pairing gametes being alike in size and activity (Fig. 9). A scries of algae can be arranged, beginning with gametes of this type, continuing step