\ 



THE SEASONAL CYCLE OF RED ALGAE 33 



reach maturity slowly, so that only a small proportion of these 

 produce reproductive bodies (tetraspores). The tetraspores, 

 however, gi\-e rise to sporelings which quickly reach maturity. 

 Of the large number of sexual plants so produced, some form 

 carpospores in abundance. 



Thus it ma}^ be seen that the entire growth of a single summer 

 may be divided into two well marked phases. The earlier, or 

 July crop, is characterized by the predominance of tetrasporic 

 individuals, whereas the later, or August crop, consists mostly of 

 smaller sexual plants, among which many large tetrasporic indi- 

 viduals, relics of the July crop, may still be seen. These old 

 specimens usually come to grief in August, at which time they are 

 torn from their supports and washed up on the beaches in large 

 quantities. The late crop, therefore, becomes increasingly sexual. 



With the approach of autumn all individuals of both these 

 generations die, not even the holdfasts remaining alive. The 

 abundant carpospores of early autumn become sporelings, of 

 which the holdfasts persist through the winter. In the early 

 summer following these give rise to the tetrasporic plants so 

 abundant at this season. The few tetrasporic plants that reach 

 maturity in late August or early September also produce spores, 

 from which sporelings arise with holdfasts sufficiently resistant 

 to last over the winter and produce the scarce sexual plants of 

 the next July. 



It is an interesting fact that the second generation (the August 

 crop of sexual individuals) is found in many species, as well as 

 in the three under discussion, on other algae ^nd on eel-grass, 

 while the first generation (the July crop of tetrasporic indi\'iduals) 

 is mostly confined to more permanent objects such as stones or 

 piles. The generation on which falls the task of overwintering is 

 that of the tetrasporic plants, which thus, in spite of their mor- 

 phological identity with the gamete-producing individuals, begin 

 to show a physiological or seasonal differentiation. 



For the o\xr whelming majority of individuals of the species 

 mentioned the following schedule holds true: 



July: tetrasporic plants release tetraspores. 



August : the second generation of smaller sexual plants matures 

 and releases carpospores. 



