452 THE AMERICAN NATURALIST. [VOL. 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, 

 '85). Guignard ('91) presented the first complete count of the 

 number of chromosomes in the life history of a plant (Li/inm 

 martagoii), 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 



