The evolution of sex in plants / by John Merle Coulter.

  • John Merle Coulter
Date:
[1914]
Catalogue details

Licence: In copyright

Credit: The evolution of sex in plants / by John Merle Coulter. Source: Wellcome Collection.

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    Although spore-formation is an effective method of producing new individuals asexually from many-celled individuals, it should not be understood that repro- duction by spores is restricted to many-celled indi- viduals. There are one-celled plants that also have spores, which means that for some reason the protoplast under certain conditions begins a series of divisions that do not involve the wall. It cannot be said, there- fore, that spore-formation was developed in conse- quence of the multicellular habit of body, but that if it had not been developed, many-celled individuals could not have multiplied asexually except by frag- mentation, which is simply body division that involves a group of cells. It would be interesting to know what conditions determine the separation of a protoplast from its wall and its abandonment of a structure it had made and kept in condition. A possible suggestion may be obtained from the occasional behavior of protoplasts when protecting themselves against unfavorable condi- tions. Among the one-celled algae it is very common for the cell wall to become thicker in response to the influence of conditions unfavorable to vegetative activity. Upon the return of favorable conditions, the protoplast abandons the thick wall, made useless for an active cell, and forms a new wall. In other cases, as among the bacteria, in response to unfavorable condi- tions the protoplast becomes separated from its limiting membrane, rounds off, condenses, and passes into a dormant stage. These protected and dormant proto- plasts of the bacteria are usually called ^spores,” but their significance is protection rather than reproduction,
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