- 306 Notes on the Blue-green Alga, etc. 
phycin granules is unknown, but they are probably composed 
of some kind of reserve substance which is produced as a 
result of the cell activities. The cyanophycin granules fre- 
quently occur in a double row, one on each side of the trans- 
verse walls in the filamentous form of the blue-green alge, 
and are especially characteristic of certain species. 
The chlorophyll is contained in the peripheral layer of the 
cell protoplasm, never in the central body, but the outline of 
this body is frequently irregular, and the peripheral chloro- 
phyll layer in contact with it takes the same irregular outline. 
The peripheral layer is sometimes regarded as a chromato- 
phore, but the evidence for this is not satisfactory, and my 
own observations do not support this view. The chlorophyll 
appears to be lodged in the meshes of the network or foamlike 
structure of the cytoplasm and frequently presents the appear- 
ance of minute granules. This may, however, be an optical 
illusion caused by the small size of the cytoplasmic meshes, 
the different layers of which, some being in focus and others 
not, when seen one behind the other, may present a granular 
appearance similar to what is observed in a very fine oil 
emulsion. 
The cell contents are sometimes vacuolate, but not usually 
so, in healthy trichomes. It is only when the cells are old and 
in various stages of decay, and in certain floating forms, that 
vacuoles appear. 
The protoplasm is in all cases surrounded by a cell membrane. 
This can be made distinctly visible by placing the plants in a 
chemical reagent, such as a 30 per cent. solution of chromic 
acid, which dissolves or destroys the protoplasm. The mem- 
brane does not give the reaction for cellulose, but is coloured 
strongly by various aniline dyes, and is probably related to 
cutin. A mucilaginous layer is frequently present outside the 
cell wall. 
In the filamentous forms the mucilaginous layer forms a 
sheath which is usually firm and leathery in Lyngbya, usually 
diffluent or mucous-like in Phormidium and some other forms. 
It differs in its chemical reactions from the cell wall surrounding 
the protoplast, being composed of a substance similar to 
cellulose. It is largely soluble in chromic acid and in strong 
sulphuric acid. The sheath can be rendered visible by staining 
in safranin and in iodine reagents, such as chlor-zinc-iodide, 
in which it often takes a blue colour. In the classification of 
the blue-green alge the sheath is used for the primary separation 
into families. 
I have found glycogen in the cells of all the blue-green 
algze which I have examined, including species from all the 
families and from a considerable number of genera, Nostoc, 
Scytonema, Oscillatoria, Lyngbya, Phormidium, Gleocapsa, 
Naturalist, 
