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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    of the bryophytes is not meant their failure as a group, for they are so very abundant that they must be called successful. The failure referred to is that the biy'o- phyte plan could not make any further progress leading to higher plants. We infer that this is true simply because the plan of the higher plants is different. In the more advanced liverworts and in mosses the archegonia and antheridia are more or less stalked above the general surface of the body. 'Phe advantage of this is seen when one remembers that the fertilized egg, thus carried up above the general surface, produces the sporophyte with its spore-case, and the spores are thus in a very favorable i)osition for dispersal by air. If this ])osition favors the spores, however, it does not favor the sperms, which must swim, for they are carried up into a position of least moisture. It is a remarkable arrangement that favors si>ores by interfering with the vei*}’ act (fertilization) that results in spores; but it works reasonably well for plants living in moist sit- uations. It is evident, however, that still larger and more leafy plants would interfere with the swimming of sperms still more. The three things which enter into this problem are food manufacture (which means display of green tissue to light and air), fertilization (which means water for swimming), and spore-production (which means e.xposure for air dispersal). In the bryophytes, food manufacture and fertilization belong to the gametophyte, and the condition that favors the one hinders the other. In other words, they are con- tradictoiy' in their demands. On the other hand, food- manufacture and spore-dispersal make the same demands for exposure, and therefore they can be coupled together