252 RELATION OF PLANT PROTOPLASM TO ENVIRONMENT. 



myxa amongst animals, we are unable to view these as surviving remnants of 

 primitive types. 



At this stage then we would suggest that far too little emphasis has been 

 placed on, and too little experiment has been conducted to extend, the value of 

 Traube's discoveries regarding colloid membranes and their enclosures. Here 

 we believe exists a wide field for study, in which the physico-chemist and the 

 physiologist might join their experimental and observational efforts with happiest 

 results. 



Let us turn our attention now to that still fairly large group of organisms 

 the Schizophyceae, Protophyceae, Cyanophyceae or blue-green algae. The writer's 

 more minute attention was directed to them when his deceased student and col- 

 league, Dr. O. P. Phillips, carried on careful and extended observations, that 

 have already been published (1). Since then he has advanced his knowledge 

 of them along various lines. 



Though synonymy and a tendency to variation, or possibly to pleomorphism, 

 have given rise to a copious nomenclature, we are probably justified in considering 

 the group to be made up of about 80 genera and close on 650 species. Of these 

 518 species are freshwater or terrestrial, 21 are brackish water, and 111 are salt- 

 water or found in saline lakes. It should further be noted that not a few of the 

 species exhibit an environmental adaptability to fresh and brackish, or to brackish 

 and salt water, or even to the first and last that is in marked contrast to the 

 behavior of most of the higher plants. We would interpret such distributional 

 features as an indication that the group originated in, and still largely adheres 

 to, a freshwater life, though as we shall presently indicate, the term " freshwater " 

 requires to be liberally interpreted. 



In form they vary from simple spherical cells that are embedded in abundant 

 mucilaginous sheaths or layers, like Glceocapsa and Aphanocapsa, to others 

 like Nostoc that form connected threads of subspherical or oval cells embedded 

 in mucilage, and again to types like Oscillatoria and Rivularia that are elongate 

 usually branching filaments, enclosed in rather thin gelatinous walls, and made 

 up of similar or dissimilar cells. In the color of the cell contents the above 

 form-groups may vary from yellow to brownish-yellow, reddish or purplish- 

 brown, red-green, purple-green or blue-green, more rarely a rich olive-green. 

 Fairly well correlated with advance in color and in general morphology, a similar 

 progress is shown in cytological detail. In simpler types like Glceocapsa and 

 Aphanocapsa, the cell-contents consist only of an outer colored zone of very finely 

 granular protoplasm, which holds the pigment above noted, and which has 

 been termed the chromatophore. Within this is a more coarsely granular mass, 

 which under high magnification suggests the existence of a finely reticular sub- 

 stance, that carries definite bodies of varying size and refraction. 



As we advance through Nostocaceous types, the main difference is that 

 reserve substances — chiefly glycogen — are not unfrequently stored in each cell, 

 but more importantly we note that definite refractive granules, which absorb 



