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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    protoplasts of a body shall ])r()ducc eggs and others sperms become i)eculiar to dilTercnt individuals, and thus individuals are sexually differentiated. At the same time, a female individual contains the male de- terminers and can transmit them, and vice versa. A visible accompaniment of this situation has been observed in certain animals and plants, which may be an index of the physiological reactions involved. The so-called A' chromosome is an extra one beyond the characteristic number for the individual. This chromo- some aj)pears in all eggs and in ajiproximately half the sperms. In the formation of a zygote, an egg may mate with a sperm having an A chromosome, or with one not having such a chromosome. The result is that the zygote contains either two A’ chromosomes, in which case it j)roduces a female, or it contains only one, in which case it ])roduces a male. In other words, it is the character of the sperm that determines the sex of the offspring. 'J'his is not an explanation, but an observx'd fact, which indicates that the selection of the sex- determiner, in the case of sexually differentiated indi- viduals, is made in the organization of the zygote; but it does not suggest, in its present form, the mechanism in those cases in which the zygote produces a bisexual individual. The only thing that can be said is that whatever determines the sexual differentiation of cells in the bisexual individual also determines the differ- entiation of sexual individuals. A feature common to the whole individual may well be determined by the zygote; but features that differentiate the cells of an individual must be determined during the development of that individual.