220 ESSENTIALS OF BOTANY 



279. Gross Structure. — Gently rub between the finger and thumb 

 a mass of filaments and note the feeling, unlike that of most fila- 

 mentous algse. 



Tease out a few filaments in a very little water in a white saucer 

 and exaniine with the magnifying glass. Note : 



(a) The color of the threads. 



(b) Their diameter. 



(c) Their length, relative to their diameter. Do they branch ? 



280. Minute Structure. — Mou.nt some bright green filaments in 

 water under a large cover-glass, examine with m.p., and note : 



(a) The form of the filaments, whether perfectly cylindrical or not. 

 (p) The division of each filament into many cells by transverse 

 partitions. Make a drawing to show these points. 

 Examine with h.p. and note : 



(c) The shape of a single cell. 



(d) The thickness and form of the cell-walls, both at the exterior 

 of the filament and in the partitions. 



(e) The cell-contents including : 



(1) Chlorophyll bands, or chromatophores. Count these. 



(2) Pyrenoids, or starch centers. 



(3) Clear cell-sap occupying most of the interior of the cell. 

 Take some Spirogyra which has been for a good many hours in 



bright sunlight. Mount a few filaments and slightly stain them by 

 running in iodine solution at one edge of the cover-glass while water is 

 withdrawn from the other edge by a bit of blotting paper. Examine 

 with h.p. and note : 



(/) The pyrenoids, small light-colored spots in the chlorophyll 

 band, each surrounded by many dark-stained starch granules. 



((/) The nucleus, a lens-shaped or ellipsoidal body, usually stained 

 brown by the iodine, and often in a position near the center of 

 the cell. 



Jlount a few filaments of Spirogyra in water under a small cover- 

 glags, run in five-per-cent solution of common salt under one edge of 

 the cover, and watch the filaments through m.p. The h.p. may later 

 be substituted. Note the manner in which the living protoplasm of 

 the cell, the jJrotojilast, shrinks away from the cell-wall. The denser 

 salt solution draws out water from the cell-sap at the interior of the 

 protoplast and thus causes the latter to shrink. The process is called 



