452 THE AMERICAN NATURALIST. [Vor. XXXIX. 
sis in plants. Strasburger’s paper of 1894 on “ The Periodic 
Reduction of the Number of Chromosomes in the Life His- 
tory of Living Organisms " (Annals of Bot., vol. 8, p. 281) was 
the first elaborate presentation of the principles of gametogene- 
sis and reduction phenomena in plants and has become classical 
as the foundation of the present attitude in botanical science 
and the basis and stimulus of a large amount of confirmatory 
research. The matter really crystallized after the discovery that 
the sporophyte generation of the higher plants possessed nuclei 
with twice the number of chromosomes characteristic of the 
gametophyte and that the reduction took place in the spore 
mother-cell just previous to sporogenesis. 
These facts were gradually established by a number of investi- 
gations beginning with Strasburger (84, '88) and Guignard ('84, 
385). Guignard (’91) presented the first complete count of the 
number of chromosomes in the life history of a plant (Lilium 
martagon), determining the reduction period to be in the spore 
mother-cell, and Overton ('93 a and b) independently reached 
the same conclusions for the same plant and extended the knowl- 
edge of the chromosome count in gametophyte and sporophyte 
to a number of other types. Overton’s paper was important in 
its suggestiveness for extended research among the higher cryp- 
togams. Other investigations followed shortly in the gymno- 
sperms, pteridophytes, and liverworts, all supporting the view 
that the nuclei of the sporophyte generation, following the fusion 
of gamete nuclei, had double the number of chromosomes char- 
acteristic of the gametophyte and that the reduction phenomena 
occurred at the end of the sporophyte generation in the spore 
mother-cell. The significance of reduction phenomena at sporo- 
genesis must be phylogenetic since it represents a return of the 
organism at this time to the ancestral gametophyte condition. 
The details of this literature belong to the account of “ Sporo- 
genesis ” and “Reduction of the Chromosomes,” and will be 
taken up later. But it is necessary to present the outline at 
this time to make clear the important fact that no reduction of 
the chromosomes takes place during gametogenesis in all groups 
above the thallophytes. 
The theories of gametogenesis among the thallophytes rest 
