The pigments 11 



The changes of colour are due to modifications of the phycocyanin, which 

 can be regarded as the ' adaptational pigment.' Gaidukov states that 

 chlorophyll is not the only colouring matter useful in the photosynthetic 

 process in those Alga3 which grow in deep water. Sauvageau ('08) does 

 not altogether agree with these views, and states that, although the rose- 

 colour of certain Myxophyceoe is due to a transformation of the phycocyanin, 

 such transformation is caused solely by the diminished intensity of the 

 light. Most of the authors who have dealt with this question appear to have 

 lost sight of the fact that red and rose-coloured Myxophycese are not confined 

 to deep waters. For instance, Oscillatoria rnbescens, which sometimes gives 

 a red colouration to large lakes, is purely a plankton species, and so is 

 Trichodesmium erytlirieuni, which colours the Red Sea. Moreover, in fresh 

 waters the red plankton species, which include certain of the Chroococcacete, 

 are mixed with others of a rich blue-green colour. There are also quite 

 a number of rose-coloured and purple filamentous forms which live in 

 subaerial habitats. 



The chlorophyll appears to be lodged in the cytoplasm in very minute 

 granules, and the carotin, when present, appears to be similarly disposed ; 

 but some doubt has been expressed as to whether the phycocyanin exists 

 in a diffuse state or is located in the same granules as the chlorophyll. It 

 seems probable, however, that it exists in a diffuse state, since it is a water- 

 soluble protein pigment of a similar nature to the red pigment of the 

 Rhodophycete. In any case, the pigments are restricted to that portion 

 of the protoplast surrounding the incipient nucleus, and the exact morpho- 

 logical interpretation of this pigmented zone has proved a matter of 

 considerable difficulty. In Glaucocystis there are true chromatophores, 

 but the presence or absence of such structures in the rest of the Blue- 

 green Algas has given rise to much discussion. 



Borzi ('86) could not demonstrate the presence of a definite chromatophore, and both 

 Stockmayer ('94) and Zacharias ('91 ; '00) have each declared that the pigmented part of 

 the protoplast cannot be considered as a true chromatophore, but only as a coloured 

 plasma. Macallum ('99) also concluded that there was no evidence of a special chromato- 

 phore. 



In contrast to these statements, Deiniga ('91) found structures in the cells of Nostoc 

 and Aphanizomenon which had the form of more or less reticulated plates in contact with 

 the cell-wall, and he regarded them as true chromatophores. Zukal ('92) also considered 

 that Tolypothrix lanata possessed a chromatophore, which consisted of a definite, demar- 

 cated part of the protoplasm, saturated with the characteristic colouring matter of the 

 plant. Fischer ('97) stated that by means of hydrofluoric acid he could dissolve all the 

 protoplast except a hollow, cylindrical or barrel-shaped structure containing colouring 

 matter, and this he therefore considered as the chromatophore. Hegler ('01) found that 

 the peripheral protoplasm was packed with granules, and he stated that each granule 

 contained both chlorophyll and phycocyanin. He therefore regarded the granules as 

 chrornatophores and termed them cyanoplasts. Kohl ('03) also regarded these coloured 



