698 



which, var. prolifera, has by maiiy authors been designated a separate 

 species, but which is most likely nothing but strongly proHferating 

 individuals, ofteii loose and lloating, growing in sheltered piaces. 



In other species, such as Rhodop hyllis dichotoma, the thailus 

 becomes almost filiform wheri it grows at the bottom of fjords, 

 but may become a centimeter broad in the open sea, as mentioned 

 above. Kjellman has given a description and sketch of this 

 peculiar narrow form (48, table XII, fig. 3). Exactly the same may 

 be said with reference to Euthora cristata, which, as mentioned 

 above, is robust with rather broad fronds in the open sea, whilst 

 these are almost filiform in fjords. According to Rosen vinge 

 (71, p. 227), similar conditions have been observed in Greenland. 



Other species are also more or less transformed in stagnant 

 water, e. g. Himanthalia lorea, the receptacles of which may be- 

 come irregularly swollen; Laminaria digitata, where the lamina, as 

 is well known, is split into a great many lobes, and which on ex- 

 posed coasts with rapid currents has a form known as f. stenophylla, 

 considered a separate species by many algologists, is often found in 

 piaces of stagnant water with its lamina undivided and more or 

 less sinuous and often urceolate in shape (f ciiciillata). The fronds 

 of Alaria escnlenta and Laminaria saccharina likewise change ac- 

 cording to the habitat. A special form of the latter, f linearis, is 

 found on exposed coasts and is remarkable for a narrow, but 

 thick and robust thailus (see fig. 85 of my flora), whereas its broad 

 forms, f. biillata and f. grandis, are found in sheltered piaces or in 

 deep water: Alaria too becomes broad in sheltered piaces without 

 currents (the narrow form from exposed coasts is drawn in my 

 flora p. 449, fig. 84). It is most peculiar, that similiar conditions 

 may aet quite differently on different species of algæ, as may be 

 seen from the preceding. I am unable to explain this satisfactorily. 



d. Temperature and Humidity of the Air. 



So far as the littoral algæ are concerned, and especially in the 

 Færoes where the littoral algal vegetation often reaches far above 

 the highest water mark, the warmth and humidity of the air are 

 naturally of great importance and may therefore be briefly men- 

 tioned liere. 



With regard firstly to the amount of heat, the average tempe- 

 rature is 6,5 '^ C. according to Willaume- Jantzen. January, the 

 coldest month, has a temperature of 3,2'^', July, the hottest, 10,8° C, 



