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.

    46/160 (page 32)
    (Fuchs), the sj)ores are eliminated, and, like animals, the reduction division is in connection with gamete- formation, and all the individuals arc alike in the num- ber of chromosomes. It should be emphasized again that two individuals are dilTerentiated whenever reduc- tion occurs in connection with spore-formation, for the difference in the number of chromosomes presently results in great differences in the appearance and func- tions of the two individuals. 'I'he above statements in reference to the origin of se.x may be summarized as follows; (1) Gametes are derived from swimming spores which have become so reduced by successive divisions as to be incapable of functioning as s])ores. (2) Gametes, when first recognized by their behavior, a])pear to be alike in ever>' visible feature, so that there is no evident distinction of sex. (3) A physiological differentiation of gametes is indicated by their mutual attraction in pairing, so that two sexes are present although not distinguishable. (4) Gametes are formed under conditions relatively unfavorable to either vegetative activity or spore- formation, but favorable to successive cell divisions, and representing the closing activity of the jilant. (5) Gametes, therefore, appear in response to unfa- vorable conditions that arise in the life history of a plant that is long enough to extend through a considerable range of var>’ing conditions. (6) The sex act results in a zygote which is formed under conditions unfavorable to vegetative activity, and therefore passes into a protected, dormant condi- tion, not germinating immediately as do the spores.