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 
