280 .lOHS. Mofl: l'KTKHSKN 



as 1 have luul no ()|)|)orluiuly ol oxamininj^ NVost's malt'rial. lii Wests 

 dcsci'iption inlormalion conccrniii}^ thc relation of tlie sliealhs to chlor- 

 zinc-iodine is lackinj«. 



/* (iiiinistissinniin iias. as far as I know, only becn found l)y G. S. 

 West and on varioiis localities: 1-^n^land, Al'rica, Antartlic rej^ions. 



Phormidium Treleasei ('.om. 



Gomont 1891) p. 37. Tilden 1910 p. 96. 



N. Icel. Hrisey, 40° C. ^7 1898 II. . I.)! Uxahver, on silicious 

 sinter at tlie hot spring, tenip. 80°; but the waler does not reach Ihe 

 alf^ie ^^7 1914V — W. Icel. Kleppjårnsreykir, hver, ^g 1914 2 sam- 

 ples. — S. leel. Heykjafos, in hot stream, lemp. 35° '^8 1914? 



Area: Arkansas (Gomont 1. e. , Canada (Tilden 1. c.). 



The linesl development of this alga was seen in Ihe samjiles from 

 Klepjjjarnsreykir where il grew at a great boiling spring which had 

 deposited a metre-high mass of silicioiis sinter, on the lop of which the 

 waler now was spoiiting. Then il ran down over ecrlain parts of the 

 silicious sinter, whereas other parts of this remained dry. On the bol- 

 tom of the oullels J\ Treleasei formed inch-thick crusls being orange- 

 brown on the surface, blue-green deeper down. The lemj). of the waler 

 35° (",. But higher up on Ihe dry parts of the sinter which, however, 

 mighl be reached by the spray when Ihe s])ring was on the boil, the 

 alga was growing in the most peculiar manner. Here it formed thick, 

 carlilaginous, slratified crusts. The uppermost layer was brown; beneath 

 this appeared a rich blue-green layer which was followed by red and 

 brown layers thai became more and more greyish inwards presumably 

 because they gradually contained more and more silica. All the layers 

 were (|uile thin. and I could count in all aboul 40. 



The various colours of the surface layers mighl |)erhaps be accounled 

 for on the basis of what we know of colour changes owing to the action 

 of the light in olher species. (Se inlroduclion p. 257). The ui)i)ermosl 

 layer, which has been exposed to the dirccl rays of the sun, mav pos- 

 sibly have been discoloured, hence the yellowish-browii colour. The 

 second layer ha<l presumably the natura! colour ol' the alga in thai the 

 intensity of the light here was so diminished tbat the colour did not 

 change. The green layer, however, acted as a lighl-filter lo the foUowing 

 layer which was thus illuminated with green light. Therefore il assumed 

 the comjjlemenlary colour and became red. The explanalion is, how- 

 ever, somewhal problematic. in thai no indicalion whalever exists of 

 this species belonging to tlujse wlio have "complementary chromalic 

 adaptation". 



("lomont has, as far as I understand his description. had this species 

 in a similar form. In Ihese samples the sheaths, which were highly 

 diflluent, coloured inlensely with chior-zinc-iodine. 



In the olher above-menlioned samples the alga rather resembled 

 P. hmuiiositin in ils mode of growth in Ihat it formed thin. membrnnous 

 layers on the silicious sinter wiliioul any stratilicalion and the leaction 

 of chlor /.inc-iodine was not so pronounced. However, 1 believe that 

 the mode of growth is lo a great extent dependent upon the external 



