THE AÉRIAL ALGÆ OF ICKLAND 425 



I have only been able to ascertain the presence of this species with 

 certainty on two palings in Reykjavik. It is, beyond doubt, much rarer 

 in Iceland tlian in Denmark and other European countries where it 

 occurs habitually almost everywliere on trce trunks and branclies, wood- 

 work, stones, and thatched roofs. 



B}^ its peculiar chromatophores without pyrenoids. its cell nucleus 

 visible already in thc living state, and above all by its zoospore forma- 

 tion it difFers so much from the other Pleiirococcus species that it may 

 beyond doubt correctly be referred to a distinct genus. This was first 

 done by Printz who (1. c.) refers it to Chodat's very doubtful genus 

 Plenrastnim iChodat 1894, p. (312\ Printz says himself (1. c. p. 22) 

 that he only »provisionally« refers it to the genus Plenrastnim and to 

 me it does not seem correct to choose this generic name, since the 

 characters which Chodat points out as the essential ones in his diagnosis 

 of the genus Plenrastnim are not found at all in P. lobatnm Printz. Chodat 

 writes about Plenrastnim (1894, p. 613) »Algue unicellulaire se reproduisant 

 par tétrades de cellules dans l'intérieur de la membrane primitive, munie 

 å l'état parfait de sculptures sur la membrane, formant des tétrades 

 compliquées pouvant se résoudre en etats gleocystis et produisant des 

 zoospores a deux cils«. The only one of the characters mentioned in 

 this diagnosis which agrees with Pleurococcns lobatiis is the last -men- 

 tioned one, that it forms zoospores. Reproduction does not take place 

 by tetrade formation within the wall of the mother cell, but by simple 

 bipartition, it has never any sculpture on the membrane, and does not 

 form any Glococijstis stage. On the whole the genus Plenrastnim is of 

 doubtful value, as Chodat himself points out (1909, p. 163), saying 

 about it »genre tout aussi mal défini et qui est a réétudier«. In Engler- 

 Prantl's Die naturlichen Planzenfam. 2. Aufl. Bd. III, p. 208, Printz 

 gives a diagnosis differing greatly from the original one given by Chodat 

 This also does not agree with the present species, it being given as a 

 generic character that there is a pyrenoid present in the chromatophore, 

 which is not the case in Apatococcns lohalns. Brand (1925) took no 

 account in his paper of the investigations of more recent authors, hence 

 he evidently did not recognise the alga before him as Plenroeoccns lohatns 

 Chod. He therefore describes it afresh both under a new generic and a 

 new specific name, calling it Apatococcns vnlgaris. The description, however, 

 agrees exactly with Plenroeoccns lohatns (Printz, too, arrived at this result 

 (I. c.)), and by staining living material of this species from the Botanical 

 Gardens in Copenhagen with Brillant blue I have convinced mysclf that it 

 shows precisely the wreath of grains round the cell nucleus (»vacuola 

 centralis seq. Brand) mentioned by Brand. There is, however, no reason 

 whatever to reject the specific name lobatns, while Brand's new generic 

 name Apatococcns is fully justified. Hence in my opinion the species 

 should now rightly be cailed Apatococcns lobatns (Chod.). 



Desmococcus vulgaris (Nag.) Brand. Brand 1925, p. 344. 

 Pleurococcns vulgaris Niig. 1849. 



— Någelii Chod. 1902, p. 281. 



Protococcus viridis Wille 1913, p. 7. 



E. Icel. 40 - N. Icel. 261 — S. Icel. 275, 276, 292 — Vestmannaeyjar 

 400, 408. 



