34 I. F. LEWIS 



September: the carpospores germinate and produce resistant 

 holdfasts. 



June: adventitious shoots appear on the tiny holdfasts. 



July: these develop into tetrasporic plants. 



Observations in the field corroborate these conclusions drawn 

 from the intensive study of a few species, and indicate that many 

 of the red algae common at Woods Hole will show on investiga- 

 tion a similar life cycle. Of these may be mentioned Champia, 

 Grinnellia, Agardhiella, Chondria, and the species of PolijsipJionia 

 other than P. violacea. 



This may be regarded as the complete and t3^pical life-cycle 

 for the New England coast, in just the same way that the com- 

 plete and typical life-history of a liverwort comprises an alter- 

 nation of sexual and asexual generations. The exceptions, how- 

 ever, which are rather rare in the liverwort {e.g. the continuance 

 of the gametophyte by means of the gemmae of Lunularia), or 

 in the ferns {e.g. the continuance of the sporophyte by vegetative 

 propagation by means of adventitious buds in Camptosorus and 

 in certain species of Asplenium) are somewhat common in the 

 Florideae. Good examples are known in Spermothamiiion 

 Turneri in New England, where sexual plants very rarely appear; 

 in Rhodymenia palmata on the Atlantic coast, where sexual repro- 

 duction is unknown; in Nemalion and many of the Nemalionales, 

 in which asexual reproduction has not been developed except as 

 the conception is involved in the formation of the carpospores 

 from the fertilized egg. A most striking example is Dudresnaya 

 at Naples. Although in Dudresnaya coccinea both sexual and 

 tetrasporic individuals are found in abundance, in the nearly 

 related Dudresnaya purpurifera only sexual plants are known. 



There are also exceptions to the separation in point of time 

 of the two generations. This separation is never of a perfectly 

 sharp and definite character, as the generations always overlap 

 to a certain extent in midsummer. Furthermore, a respectable 

 minority of sexual individuals is always present even when the 

 asexual plants are most dominant, and vice versa. In some species 

 the two generations occur side by side so that neither is dominant 

 at any season. Such species are Ceramium ruhrum and Corallina 

 officinalis, both of which occur at all seasons. 



