404 ELEMENTARY BIOLOGY. [CHAP. 



a. Note that each filament is composed of a series 

 of cylindrical cells, that it is unbranched, and that 

 all its cells are alike (apart from slight differences 

 of length). Observe especially that there is no 

 difference of structure between the two ends of 

 the filaments. 



b. In each cell observe 



a. The cell-wall, completely surrounding the cell. 

 It consists chiefly of cellulose and gives the 

 same reactions as the cell-wall of Protococcus 

 (p. 393). On treatment with potash solution, 

 the stratification of the cell-wall can be made 

 out with a high power. 



y8. The protoplasmic primordial utricle, completely 

 lining the cell-wall on the inside. This is 

 colourless and appears finely granular under 

 a very high power. In order to see the 

 primordial utricle better, plasmolyse the cell by 

 running in 10 p. c. salt solution. The prim- 

 ordial utricle will now contract away from the 

 cell-wall and be easily seen. 



y. The bright green spiral chromatophores. These 

 are from i to 10 in number, according to 

 the species. Observe the roundish bodies 

 occurring at intervals in each chromatophore. 

 These are the pyrenoids, each of which is 

 surrounded by a layer of starch-grains if the 

 plant has been exposed to light. Run in Iodine 

 solution to demonstrate the presence of starch. 



B. The large vacuole occupying the greater part of 

 the interior of the cell. 



c. The nucleus in the middle of the cell. In most 



