32 



and then a specimen richly provided with the named organs, and 

 all the other ones from the same place and time quite sterile. 

 Specimens collected in autumn, winter and spring have novv and 

 then been fertile, but still the greater number sterile. Thus the 

 development of the reproductive organs, at least in some of the 

 species, with us probably takes place nearly all the year, but in 

 proportion to the number of individuals always in apparently few 

 of them. Only a couple of species are more commonly to be 

 found fertile in summer. I have examined hundreds of specimens 

 of other species from different localities and at different seasons, 

 but only met with a couple or very few ones bearing the named 

 organs, and those not well developed. In species, by which the 

 conceptacles of sporangia alwa}^ grow down into the frond, I 

 often also met with specimens with the very greatest number of 

 branches not showing overgrown conceptacles. I am, therefore, 

 inclined to suppose, that at any rate in some of the branched 

 species, and especially specimens much attacked by animals, the 

 development of the organs of propagation in all rather seldom 

 takes place. Moreover, from a certain age the plant appears not 

 to develop reproductive organs, though the vegetative part still 

 continue its growth, the plant being alive. 



The crustaceous species are on the other hand more com- 

 monly furnished with organs of propagation, mostly sporangia. 



The named organs after being founded appear in their further 

 development also to be checked by attack of animals, especially 

 the conceptacles of sporangia. but probably also those of antheridia 

 and cystocarps. I have seen rather numerous superficial concept- 

 acles of sporangia filled with animals or animal substance, and 

 still more overgrown, many of which apparently attacked before 

 growing down into the frond. Besides, the sporangia themselves 

 may often be infested with small perforating algæ, or animals. 



The colour of the Lithothamnia also is subject to much va- 

 riation. In deep water it nearly always seems to get darker than 

 in more shallow, but, on the other hand, less varying. Growing 

 in shallow water especially with sandy or else light bottom it gets 

 ven 7 light, and the part turning upwards even whitish in summer, 



