450 THE AMERICAN NATURALIST. [Vol. XXXIX. 



large number of studies of nuclear figures in antheridia and 

 archegonia, the generative cell of the pollen tube and micropylar 

 region of the embryo-sac. There are no reduction phenomena 

 in these higher groups at the period of gametogenesis. 



The subject is complicated in some types of spermatophytes 

 where the gametophyte phase is so reduced that the mitoses 

 which precede gametogenesis may follow immediately upon the 

 two mitoses characteristic of sporogenesis or be separated from 

 them by only one or two divisions. For example, it is known 

 in several types of the lily family (Lilium, Tulipa, Fritillaria, 

 Erythronium, etc.) that the two mitoses of sporogenesis (hetero- 

 typic and homotypic) are included in the embryo-sac and become 

 a part of that gametophyte history. The third and final mitosis 

 in this history differentiates the egg in the micropylar end of 

 the embryo-sac and is a typical nuclear division. This subject 

 was treated in some detail in Section III of these " Studies " 

 {Amer. Nat., vol. 38, pp. 741-745, 1904). When the mitoses of 

 sporogenesis are not included within the embryo-sac we find 

 almost without exception three typical mitoses preceding the 

 differentiation of the egg in the angiosperms and a very large 

 number in the gymnosperms, and of course in the pteridophytes 

 and bryophytes the whole vegetative period of the gametophyte 

 which is generally green and self-supporting. There are from 

 two to three mitoses in the pollen grain and male gametophyte 

 of the angiosperms before the development of the sperm nuclei 

 and a somewhat larger and more variable number among the 

 gymnosperms. It is necessary at the outset to understand 

 clearly what are the events of gametogenesis in spermatophytes 

 because several authors have carried the phenomena of sporo- 

 genesis over into the period of gametogenesis, where it can, 

 have no proper place in exact morphology. Such papers will 

 be treated in connection with " Sporogenesis " and " Reduction 

 of the Chromosomes," for they concern primarily these phe- 

 nomena alone. 



Gametogenesis must be considered at present chiefly from 

 our knowledge of the conditions in the higher plants as they 

 furnish almost the only detailed information that we have on 

 the subject. Upon this as a basis we are justified in suggesting 



