472 THE AMERICAN NATURALIST. [Vol. XXXIX. 



presents three mitoses after those of sporogenesis before the 

 egg nucleus is formed. But in a number of types in the hly 

 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 

 oogenesis 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 

 {e. g., Lilium, Tulipa, Fritillaria, Erythronium, etc.). Search 

 among some of the most highly speciahzed MonocotyledonEe may 

 actually reveal examples of the complete suppression of the 

 female gametophyte. 



