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THE AMERICAN NATURALIST [Vol. XL! v 



present strong evidence in support of the theory of alter- 

 nation of generations in the Ehodophyceae. The peculi- 

 arity of Rlwflt/nipuia pahnata on the Xew England coast, 

 referred to above, may likewise rest upon a suppression 

 of reduction phenomena in the tetrasporangium which 

 would lead to the omission of the sexual phase from the 

 life history and permit of an indefinite succession of 

 tetrasporic plants. 



It is very important that the life histories of some of 

 the simpler red alga? be investigated, especially such 

 forms as have Chant ransia-Mke stages characterized by 

 the production of monospores. The fact that the reduc- 

 tion divisions of Polysiphonia and Grifiithsia are not as- 

 sociated with the formation of carpospores leads one to 

 suspect that the period of chromosome reduction in such 

 types as Batrachospennum and Nemalion may occur at 

 the time of the germination of the carpospore. Should 

 this prove to be the case, the origin of the tetrasporic 

 phase, characteristic of the higher Rhodophyceffi, may 

 without difficulty be conceived as the result of a post- 

 ponement of the reduction divisions and their associa- 

 tion with a type of cell similar to and perhaps identical 

 with a mono sporangium. Such a postponement or 

 delay in the expression of the reduction divisions would 

 establish at once a plant with the diploid number of chro- 

 mosomes (tetrasporic plant) and introduce into the life 

 cycle the tetrasporangium as a new type of reproductive 

 organ. 



Lewis regards the tetrasporic plant as illustrative of 

 "an homologous alternation of generations, not the 

 equivalent, wholly or in part, of the sporophyte of the 

 archegoniates", and he thereby limits the sporophytic 

 phase in the life history to the sporogenous cells of the 

 cystocarp. This conclusion is based on the morphological 

 resemblance of the tetrasporic plants to the sexual, al- 

 though Lewis himself points out important differences 

 between the two. Thus "tetrasporic plants (of Griffith- 

 sia Bornetiana) are always more abundant, as well as on 



