DISTRIBUTION 133 



Borgesen calls it the Hildenbrandtia formation, after the 

 little red alga, Hildenbrandtia, which predominates in 

 it. Such formations and associations can vary end- 

 lessly in the different seas, according to the nature of 

 the bottom, the salinity of the water, etc. ; Svidelius 

 has even described, for the Baltic, two detached assoc- 

 iations of Phyllophora and Fucus at a depth of 4 to 

 5 -5 fathoms, of which the detached specimens are 

 absolutely sterile and far narrower than the attached 

 plants, growing at a considerable distance, from which 

 the loose ones have been derived. A thorough know- 

 ledge of the formations and their components on a given 

 coast is the corner-stone of the study of the geographical 

 distribution of algae, so interesting in itself because it 

 may help us to reconstruct the former aspect of the 

 globe. By a careful study of the algae of the Baltic 

 and Arctic Seas, Svidelius arrived at conclusions which 

 strengthen the already existing views of zoologists 

 about a connection of those seas in the Glacial 

 Period. Borgesen has given beautiful photographs 

 of various formations occurring on the coast of the 

 Faeroes. 



How much might be done in this line if some of the 

 many photographers of our day took to photographing 

 algae ! The field is still new, and might tempt a spirit 

 keen to surmount difficulties. 



It is impossible to give in a few pages a systematic 

 survey of so large a group as the algae ; their systematic 

 arrangement can be studied in books written for that 

 purpose. I will only name the principal divisions, and 

 give their most striking characteristics that are of 

 value for the collector. I will add some figures of very 

 common or very striking algae, and treat a little more 

 in detail a few families. The questions touched upon 

 will show how interesting those families are, but' other 



