. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . only of the intercellular portion of theinvestment. This may also be true with regardto the supposed protoplasmic connections betweenthe cells of Nostoc and other genera. Gardner(06) entirely failed to demonstrate any proto-plasmic continuity between the cells in the variousforms he examined. In certain species of Stigonema the proto-plasmic connections are rather more conspicuousthan in other blue-green forms, a condition beingpresented whic
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . only of the intercellular portion of theinvestment. This may also be true with regardto the supposed protoplasmic connections betweenthe cells of Nostoc and other genera. Gardner(06) entirely failed to demonstrate any proto-plasmic continuity between the cells in the variousforms he examined. In certain species of Stigonema the proto-plasmic connections are rather more conspicuousthan in other blue-green forms, a condition beingpresented which is precisely similar to the proto-plasmic continuity exhibited by the Rhodophycese(W. & G. S. W., 97 A, p. 242; G. S. W., 04).The continuity is effected by a single protoplasmicstrand connecting the polar extremities of adja-cent cells. The strands are by no means smalland they pass through centrally-placed pores inthe transverse walls of the filaments. The poresare best seen in the young branches of Stigonemaocellatum, particularly if plants previously driedare soaked in water, or if the protoplasts arecaused to shrink by means of Fig. 10. End of trichome ofCylindrospermum sp. showingthe terminal heterocyst andspore furnished with hair-likeprocesses, and the gelatinoussheath frayed around theheterocyst. The protoplas-mic connections are alsoshown through the commu-nicating pores in the end-walls of the cells. Very highlymagnified (after Phillips). HETEROCYSTS. In the filamentous families of the Nostocaceas, Scytone-maceas, Stigonemacese, and Rivulariacese, there are certain differentiatedcells known as heterocysts. They may be sparsely scattered in an intercalary Heterocysts 17 manner between the vegetative cells of the filament (hg. 11 C), or theymay be terminal (fig. 11 F and G), Sometimes they are seriate as insome species of Tolypothrix, Calothrix, Nostoc, etc. As a rule, they area little larger than the vegetative cells, and in most cases stand outconsp
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