741 



instance at Troldhoved, the Phymatolithon-formniion (see page 750) 

 is foiiiid at about low water mark or a little above; but on rowing 

 into the cave, it will be found to extend l'urlher and further up, till 

 far above the highest water mark. This alga is of a fine pink 

 colour in the cave, and, as far as I have seen, reaches further into 

 the cave than any other alga; darkness of course gets the belter 

 of it at last. Together with Phymatolithon, wc often find Cruoria 

 pellita forming large, shining, dark reddish incrustations, even far 

 above the lowest water mark. Other sublittoral algæ found here are 

 Delesseria siniiosa and even Delesseria sangiiinea the thailus of which 

 is torn by the surge into narrow lobes. One may moreover find 

 Odonthalia dentata, Plocamiiim coccineiim, Lomentaria clavellosa, Pti- 

 lota pliimosa, Eiilhora cristata, and, just below the lowest water 

 mark, the beautiful Pterosiplionia parasilica and many more sub- 

 littoral algæ. 



As mentioned above (page 701, footnote), some sublittoral algæ 

 may hardly ever be found at the level of the sea, not even in the 

 caves, and as likewise pointed out at the same place, this must 

 be ascribed most probably due to the surge, as several of these 

 algæ are found in other piaces at the lowest part of the littoral 

 region. 



This peculiar circumstance, that a deep water- flora can be 

 found at the level of the sea in caves, has however already 

 been pointed out by several algologists. In the introduction to 

 his algæ-flora (18, p. 220 — 221) Falkenberg speaks of a >Grotta 

 del Tuono« in the neighbourhood of Naples, with only very shal- 

 low water, which was constantly renewed by its connection with 

 the sea. He says: »Trotz des niedrigen Wasserstandes in die- 

 sem Bassin finden sich hier an den dunkelsten Stellen Algen, die 

 sonst als charakteristische Pflanzen einer Tiefe von etwa 50 — 60 

 Meter im Golfe sich finden.« And after having named a certain 

 number of the algæ found in this place, he continues: »So zeigt 

 diese kleine Grotte mit flachstem Wasserstande in ihrer Algen- 

 vegetation je nach dem grosseren oder geringeren Grade von Dun- 

 kelheit einen åhnlichen Wechsel, wie er im freiem Meere bei dem 

 Uebergang aus grosserer in geringere Tiefe stattfindet«. In the 

 section on the influence of the different degrees of the intensity 

 of light on the distribution of the marine algæ, Bert hold points 

 out that the algæ without exception must, as independent assi- 

 milating plan Is, require a certain intensity of light, yet different 



