66 THE PLANT WORLD. 



than that. Apart from the Theory of N^atural Selection, no 

 modern hypothesis of evohition has been so helpful or so likely 

 to stimulate further work. " * * " q g_ Gager. 



It has been known for many years that the life cycle of 

 the higher plants is divisible into two parts, one of which con- 

 stitutes the sexual generation, and the other the asexual gen- 

 eration. These two phases in the life cycle are usually not 

 distinct but merge into one another in a manner now familiar 

 to every botanical student. In the ferns, however, the generation 

 bearing the sex cells is inde|)endent from the one bearing the 

 asexual reproductive bodies, the spores. In the lower orders 

 of plants there is more difficulty in determining whether 

 this alternation of generations really exists, and we are 

 only now beginning to learn concerning this matter in such 

 forms. Our knowledge of the life history of the plants of the 

 ocean, particularly of the algae, is very limited indeed. For 

 instance, probably not more than three of four of the red 

 algae have been studied at all thoroughly from this point of 

 view. Accordingly, any contribution to our knowledge of the 

 life history of these obscure forms is welcome. 



There has lately appeared an extensive study by Shigeo 

 Yamanouchi (Bot. G-az. Dec. 1906) on Polysiphonia violaceae, 

 one of tlie red algae growing in the vicinity of Woods Holl, 

 Massachusetts. Yamanouchi finds a clearly marked alternation 

 of generations in this alga. The spore bearing plant closely re- 

 sembles the one which bears the sex cells but is quite distinct 

 from it. Twice as many chromosomes is found in the nuclei 

 of the asexual plants, those bearing the tetraspores, as are in 

 in the nuclei of the opposing generation ; the former are, there- 

 fore, true sporophytes and the latter true gametophytes. This 

 state of things is homologous to that existing in the ferns and the 

 type of alternation of generations is clearly "antithetic." The 

 red algae are thus the lowest forms of plants in which an asex- 

 ual phase is interpolated in the life history and in this particular 



