30 



observed to form a scum on the .surface of the water. The contents of each coccus divide 

 into two and the original wall stretches out and becomes partially gelatinous. Then 

 further divisions ensue, resulting in the formation of a coiled thread within the 

 wide envelope. This thread may be set free by the complete gelatinization of the 

 envelope. 



POLYMORPHISM. At one time it was generally assumed that the Blue- 

 green Algae exhibited a considerable polymorphism, and that many of 

 the described genera and species were merely stages in rather obscure life- 

 histories. Modern investigations, and especially the methods of pure culture, 

 have shown that this belief was a fallacious one, and that the amount of 

 polymorphism in the group is really very small'. 



The sweeping statements of Itzigsohn, Hansgirg and Wolle that the 

 members of the Chroococcacea3 were merely stages in the development 

 of higher forms of the Blue-green Alga3, were only assumptions based upon 

 crudities of observation. That such ideas gained credence was due very 

 largely to the general habit of so many of the Myxophycese in occurring 

 for the niost^part in gelatinous masses and strata. Thus, it is usual to find 

 various members of the Coccogonese and Horrnogonese as components of the 

 same stratum, simply because they require the same conditions of environ- 

 ment and their mutual association more effectively results in the attainment 

 of the necessary conditions. 



No purpose would be gained by recapitulating any of the published 

 statements of Hansgirg, Zopf, Zukal, or others concerning this supposed wide 

 polymorphism. It is sufficient to say that pure cultures, and other carefully 

 conducted experiments, furnish no evidence in proof of the suggested generic 

 or specific identity of many of these forms which live intermingled in a 

 common gelatinous matrix, and to the skilled observer with a thorough 

 taxonomic knowledge of the group, there is rarely much difficulty in dis- 

 criminating between the developmental stages of the higher types and the 

 unicellular or colonial plants of a lower type (G. S. W., '04). 



OCCURRENCE AND DISTRIBUTION. The Myxophyceae have a world-wide 

 distribution, occurring in abundance in all climates which are sufficiently 

 moist. The majority of the known forms are either subaerial or freshwater, 

 but some occur in saline or brackish areas, and other littoral forms are 

 frequent on nearly all coasts. Many species are prominent constituents 

 of the plankton of freshwater lakes, and a few occur in the marine plankton 

 of the warmer seas. Some of the Chroococcacese are free-floating organisms 

 in bogs and lakes, but many of them form gelatinous masses on wet and 

 dripping rocks. Often the gelatinous mass is spread out as a stratum 

 of a blue-green, violet, red-violet or grey colour. In parts of Western 

 Scotland and the Hebrides Glceocapsa magma occurs in vast quantities on the 



