702 



ravs which they especially need, already become fainter at a 

 small depth. The red algæ grow deepest, as they need the green 

 rays, occurring at greater depths, the most; fmally the brown 

 algæ are specifically fitted for growing at a depth between that 

 of the green and the bluish-green algæ on one side, and that of 

 the red algæ on the other side. He calls our attention to the 

 faet, that the algæ are very well able to accommodate themselves 

 to the colour of the light of their habitats. He refers to the 

 interesting observation made by Nadson, that certain Cyanophyceæ 

 and Chlorophijceæ are represented by green specimens, near the 

 surface of the sea, and by red, in deep water. This may also 

 happen on the coasts of the Færoes, as I have already men- 

 tioned. Nadson thinks for instance, that Conchocelis rosea is a 

 deep water form of Ostreobium Oiiekettii. 



Bert hold and 01 tm an ns determine the Florideæ as shade 

 piants, but this is criticised by Gaidukow, who asserts that Olt- 

 mann's experiment only confirms Engelmann's theory, that the 

 Florideæ of deep water have the typical colour of the Florideæ, be- 

 cause they grow in green and blue light, whereas they turn brown 

 and yellow near the surface in the white light ^ 



The Engelman n- Gaidukow theory on the whole coincides 

 with my observations ; still it seems to me that the quantitj^ of the 

 white light must practically be of no small importance not only 

 to the colour of the algæ, but also to their distribution. On the 

 coasts of the Færoes, on the beach, and even above it, a great 

 many Florideæ of a deep red colour are found, perhaps some- 

 tiraes of a more reddish-brown, but I have hardly ever seen them 

 turning almost light yellow as the same species do, for instance, 

 on the west coasts of Norway or on our own coasts^. No doubt 

 this is due to the weaker light at the Færoes, where fogs are fre- 

 quent, and the sky much overcast; and as a vegetation of Flo- 

 rideæ, typically red and including some of the forms usually 

 belonging to great depths, is often found in small inlets between 

 Thorshavn and Arge, in water not even 2 fathoms deep and 

 overshadowed by Laminariæ, this is certainly also due to the 



^ In the West Indies Florideæ growing in shallow water, exposed to direct 

 siinlight, are often perfectly green, or bluish-green, e. g. Grateloiipa filicina. 

 Svedelius has observed the same faet on the shore of Ceylon (compare: Bot. 

 Notiser. 1905, p. 181). 



* On one occasion I found Porphijra nnibiUcalis turning 3-ellow, in tlie 

 sounds north of Kvalvig. 



