. Morphology of angiosperms (Morphology of spermatophytes. Part II). Angiosperms; Plant morphology. THE MICROSPOBANGTUM 31 the mother-cell stage was found in September, and fully formed pollen in the spring while the ground was still frozen. Dug- gar-' has also observed that the rnierosporangia of SympJo- carpus pass the winter in the mother-cell stage. The pollen mother-cells of Podophyllum peltatum are forming the tetrads when the young plant has reached the surface of the ground, so that in all probability the winter is passed in the mother-cell stage. Although Conrad 29 found stamens well
. Morphology of angiosperms (Morphology of spermatophytes. Part II). Angiosperms; Plant morphology. THE MICROSPOBANGTUM 31 the mother-cell stage was found in September, and fully formed pollen in the spring while the ground was still frozen. Dug- gar-' has also observed that the rnierosporangia of SympJo- carpus pass the winter in the mother-cell stage. The pollen mother-cells of Podophyllum peltatum are forming the tetrads when the young plant has reached the surface of the ground, so that in all probability the winter is passed in the mother-cell stage. Although Conrad 29 found stamens well formed in the winter buds of Quercus velutina, the tissue of the anther was still homogeneous. These records mere- ly serve as an indication of what may be expected when the subject is really investigated. It is evident that the time elapsing between the differentiation of the archesporium and pollination is often much longer than has been ordinarily supposed. It would seem probable that in gen- eral those plants whose flowers open early in the season, as most trees and the vernal herbs, develop their rnierosporangia before the end of the " growing season,'' and that the mother-cell stage is the usual win- ter condition. In the case of such plants, therefore, the earliest stages in the history of the rnierosporangia must be looked for during the latter half of the growing season that pre- cedes the season of " ; This suggests that the natural end of a growing season for the sporophyte is the attainment of the mother-cell stage by its spo- rangia, which is really the limit of the sporophyte in the alterna- tion of generations ; and the natural beginning of the next season is the reduction division and the beginning of the gametophyte. Of course such a distinction disappears in many plants whose seasonal habits are different from those we have been consider- ing, but it suggests a natural division of growth between seasons, and even in annuals the mother-c
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