258 JOIIS. lUrtK l'KTKHSKN 



foiiiul Ihal only a \o\\ \)cri-cn[i\^c ol" Ihe s|)ec"ics iii (|iu'slion slunv 

 "rlmnnalif adaplalioii' iii dillerenl coloured lif^hts. Tluis Harder 

 (I. c.) Ibund that amoiig 50 species 2 only had Ihe slaled capacily. 

 Boresfh (H)ltl, \). 'M')) Ibund thai Ihe colour variations were due 

 to (hllerenees of Phycocyanin, whilst Chiorophyll and (>arotin were 

 not atleeled i)y llu' inonochronialic- hghts. 



Boresch (1910), Magnus and Schindler (1912) and Schindler 

 (1913) demonslraled thai in Agar-cullurcs Ihe colours ol' llic hlue- 

 grecn algae varied when the nitrogen was exhausted, this pheno- 

 nienon lioresch nanied "StickslolTchlorose ". Quite a nuniher ol" 

 varying tints mighl appear under the chlorose. These observations 

 are also conlirnied by Maertens (1914) and E. G. Pringsheim 

 (1912, 1913). 



Horcsch (1920, 1921) has l'urther proved that absence of iron 

 in the cullures produce siniilar chlorotic conditions as lack of ni- 

 trogen. Violet, brown or yellow tones and the transitions between 

 theni occur. With regard to the iron chlorose, Boresch further 

 proved that Ihe Chiorophyll and the Phj'cocyanin gradually dis- 

 appears from the celis so that linally only the Carotin remains. 



The (juestion as to whelher such colourations of the Cijano- 

 phijceæ caused by cxternal conditions are to be met with in nature 

 to such an exlent that the use of colour as a distinctive feature in 

 the (Ajdnophijceæ is thereby precluded, is of great interest. Giinther 

 Schniid (1917) has already attenijjted lo solve this question, but 

 he arrives at a negative conclusion, in that he seems to consider 

 the conditions governing Ihe devialing colourations in the cullures 

 to be of such a descriplion that thev hardlv can be ibund to anv 

 appreciable extent in nature. I am of the opinion thai further in- 

 vestigalions must be awaited, and that for the present an altempt 

 should be made lo ascertain, more accuralely than hilherto, Ihe 

 colours in Ihe various species of the (jidnoplujccd- under varying 

 conditions in order thereby lo obtain a more reliable basis for Ihe 

 solution of this (piestion. For Ihe determination and ascerlainmenl 

 of the colours Gunther Schmid (I. c.) recommends Klinksieck 

 et Val et te: Gode des couleurs, Paris 1908, as a serviceable aid. 

 The references (Codex number) given in the syslemalic part of this 

 work refer to the book in (juestion. I nnisl add. that 1, in conlrast 

 to Schmid, have used the colours in a dry condition as all my 

 colour determinations have been made on dried malerial. 



I have carried out a number of colour delerminalions by means 



