37i 
Life-history of Anabaena Cycadeae. 
The cellular investments of the cyanophyceous cell are quite unique. 
They are, however, difficult to recognize in the unstained condition, hence 
Kiitzing and Borzi thought that the protoplast was bounded merely by 
a plasmic membrane inside the mucilaginous sheath. Gomont and Kirchner 
demonstrated the presence of a definite membrane in all cases, and Fritsch 
more recently gives a detailed account of the cellular investments, with 
which the following observations on Anabaena Cycadeae are in accordance. 
The external mucilaginous sheath (Fig. 3, m.s .) is comparatively narrow, 
and remains unaffected by any stain used, except vesuvin, which renders it 
brown. It is, however, distinctly visible both in stained and unstained 
preparations as a highly transparent, refractive zone surrounding the cell. 
This mucilage ceases to be secreted by the heterocysts, consequently it is 
only found enveloping these in their early stages of development (Fig. 3). 
Each protoplast, when fully formed, is typically provided with two 
investments. In very young filaments, however, there is only a colourless 
investment present, which becomes evident when the external mucilaginous 
sheath is stained brown by vesuvin (Fig. 4). It is convenient to call this 
membrane the inner investment, and in older cells between it and the 
mucilage there is a small cylindrical sheath known as the outer investment 
(Fig. 3, o.i). The adjacent cells of a filament are separated by a trans- 
parent colourless band, the transverse septum (Fig. 3, t.s.), which has 
slightly concave lateral limits, and distinctly separates the outer invest- 
ments of the two cells ; the latter have well-defined lateral portions, but 
these are joined by much less readily discernible transverse membranes. 
Gomont found that a 33 % solution of chromic acid dissolved away the 
greater portion of the protoplasmic contents, leaving the cell membranes 
intact. This was indeed found to occur except in some very young vege- 
tative cells where the definition had been somewhat lost. The cyano- 
phyceous cell membrane is quite unlike that of any other Algae, apparently 
being of a very rudimentary type of development, and of a viscous muci- 
laginous nature, while it is capable of offering great resistance to oxidizing 
agents, and at the same time possessing remarkable elasticity, as shown by 
Brand’s plasmolysis experiments. Kohl has demonstrated the presence of 
chitin, cellulose, and pectin in the membrane. The presence of the latter 
is clearly indicated by its absorbing Ehrlich’s haematoxylin and remaining 
unaffected by chloriodide of zinc, and also iodine followed by dilute sulphuric 
acid. Iodine renders the outer investment dark brown, but the inner one 
remains clear and transparent. 
In Anabaena Cycadeae the cytoplasm extends from the cell-wall to 
the central body, and although the peripheral layers contain the pigment 
and are undoubtedly the centre of assimilative activity, there does not 
appear to be any definite chromatophore present. 
Many observers, amongst whom are Stockmeyer, Zukal, Zacharias, 
