472 THE AMERICAN NATURALIST. | (Vor. XXXIX. 
presents three mitoses after those of sporogenesis before the 
egg nucleus is formed. But in a number of types in the lily 
family (e. g., Lilium, Tulipa, Fritillaria, Erythronium, etc.), the 
mitoses of sporogenesis are actually included in the embryo-sac 
and the very next mitosis, which is typical, differentiates the 
egg (see Section III, Amer. Nat., vol. 38, pp. 741-744, Oct., 
1904). This is the furthest point attained in the reduction of 
the gametophyte which in such forms actually includes but a 
single nuclear division, in its history. But however close the 
mitoses of sporogenesis come to those of gametogenesis it is 
perfectly clear through the long phylogenetic history in the 
lower spermatophytes, pteridophytes, and bryophytes that the 
two are morphologically distinct processes and are always sepa- 
rate. It is unfortunate that the terms spermatogenesis and 
oögenesis should be applied to processes of sporogenesis as has 
been done by several authors, for such usage involves a confusion 
of two events which phylogeny clearly shows to be different in 
origin and to have back of them the diverging history of sporo- 
phyte and gametophyte from the times of thallophyte ancestry, 
the most remarkable evolutionary history in the plant kingdom. 
It is conceivable that some plants may finally reach a stage in 
their evolutionary history when all the gametophytic mitoses in 
the pollen grain and embryo-sac will be suppressed and the 
nuclei resulting from sporogenesis become gamete nuclei. But 
it is clear that in such an event the gametophyte phase would be 
obliterated and we should have an entirely new type of life 
history. There would then be only one organism (derived from 
the sporophyte) whose gametes would be formed immediately 
with the differentiation of the pollen grain and  embryo-sac. 
Such an organism would present reduction phenomena with the 
differentiation of the gametes and its type of life history would 
be identical with that of animals. We should look for such a 
reduced life history in groups related to forms in which the 
mitoses of sporogensis are included in the embryo-sac and the 
gametophyte phase is represented by a single nuclear division 
(c. g, Lilium, Tulipa, Fritillaria, Erythronium, etc.. Search 
among some of the most highly specialized Monocotyledonze may 
actually reveal examples of the complete suppression of the 
female gametophyte. . 
