H. jonsson: marine algal vegetation 167 



A. Annual algae. The annual species are especially the Green 

 Alga? which grow in the upper littoral zone and are exposed during 

 each low-tide. The upper littoral zone is that part of the algal region 

 where the change of seasons is most felt and where winter prevents 

 many species from continuing life. Such species then produce spores 

 which live through the winter as such, or in the early stages of 

 germination. Of annual species the following may be mentioned: — 



Codiolura gregarium. Ulothrix-species. 



C. pusillum. Ulvella. 



Percursaria. Pringsheimia. 



Enteromorpha-species. Urospora-species. 



Monostroma-species. Chaetomorpha tortuosa. 



Prasiola-species. Spongomorpha vernalis. 



Cladophora-species. 



In addition, some of the endophytic species must be regarded 

 as belonging to the annuals, although some of them can be met 

 with at all seasons of the year. As examples of such species may 

 be mentioned : — Chlorochytrium-species and Codiolum Petrocelidis. 



The life-periods of the species mentioned above are probably 

 of different lengths and it is possible that some of them can pro- 

 duce several generations during one summer (cf. Borgesen, 11 

 and 12). The majority of these species grow luxuriantly during 

 spring (March — May) and summer (June — August), produce spores 

 at the end of summer and then die. Some of them, however, con- 

 tinue life into the autumn (September — November), or at any rate 

 until September. A few may also be met with during winter (De- 

 cember — February), e. g. Enteromorpha intestinalis f. prolifera, Mono- 

 stroma fuscum (sterile and fruiting), Cladophora rupestris (abundantly) 

 and Cladophora sericea (sparingly). 



Of the above-mentioned endophytic species I shall refer to 

 Chlorochytrium inclusum and Codiolum Petrocelidis only. Both these 

 species occur at all seasons of the year. They are found most fre- 

 quently in the host-plants in the sublittoral zone, where the conditions 

 of life must be considered to be more stable than in the littoral 

 zone. I regard such species as short-lived. They are found all the 

 year round, as probably several generations are produced during 

 the year. 



Among the annual Brown Algae the following must be in- 

 cluded: — Myrionema-species, Ascocyclus and the majority of the 

 Ectocarpaceoe , Leptonema, Litosiphon, Isthmoplea, Phatostroma, Ca- 



