2 TORREYA 



with the gametophyte, which was the original structure. The other school 

 of thought has maintained that the two generations are parts of an original 

 gametophytic generation, one part of which became spore-producing while the 

 othei part retained its gamete-producing function, thus giving rise to genera- 

 tions which are homologous in origin. The term homologous alternation of 

 generations is used in two ways, however ; in one sense to indicate the homolo- 

 gous origin of the generations and in another sense to indicate generations which 

 are alike in appearance (isomorphic). It is not the purpose here to review the 

 merits of the antithetic and homologous theories of alternation. Most of the 

 references are to older literature and will be found in Svedelius (1927) as 

 well as in current textbooks on plant morphology. The bearing of the present 

 concept on the problem will be referred to in the latter part of this paper. 



The phase of the phenomenon which has been widely accepted and which it 

 is here considered may need revision is the application of the term "asexual" 

 to the sporophytic generation and to its characteristic and "normal" method 

 of reproduction, that is, by spores produced by the process of meiosis. This 

 usage may depend, in the first place, upon one's definition of or understanding 

 of what constitutes sexual and asexual reproduction. If the term sexual re- 

 production is to be used only to refer to the initiation of a new individual or 

 generation of a life cycle by the fusion of cells, and if asexual reproduction is 

 to be used to include all cases in which a new individual or a generation of a 

 life cycle is initiated without such fusion, regardless of whether the same or 

 another generation is thus initiated, then, by definition, the alternating genera- 

 tions in the life cycle of plants are sexually and asexually reproducing genera- 

 tions. Sexual and asexual reproduction have long been considered in the above 

 manner, this is, the former as being characterized by a fusion of cells and the 

 latter by a lack of fusion. 



Selecting from the older literature we find the viewpoint that the sporo- 

 phyte and gametophyte represent, respectively, asexual and sexual genera- 

 tions concisely expressed in an oft-quoted paper by Davis (1903). "The game- 

 tophyte is the sexual plant, developing the sexual cells or gametes. The sporo- 

 phyte is asexual, producing spores." However, if we continue to follow the 

 discussion in the same paper, we find expressed the state of knowledge which 

 existed at that time concerning the chromosomes and their behavior. "If 

 the question is asked why are the chromosomes so important and why should 

 their number be so significant, no answer can be very satisfactory for our deep 

 ignorance of the nucleus is exposed." "We do not know what the chromosome 

 does " "It will thus be seen that there can be no genetic relationship be- 

 tween the reduction phenomena of higher plants and animals. They are not 

 found at the same points in the life history and there are also fundamental 



differences in the details of the process ." " there is no reduction 



phenomena in plants at the time when sexual cells are formed ." "The 



