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 alge. 
Tease out a few filaments in a very little water in a white saucer 
and examine with the magnifying glass. Note: 
(a) The color of the threads. 
(6) Their diameter. ; 
(c) Their length, relative to their diameter. Do they branch? 
280. Minute Structure.— Mount 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. 
(6) 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. 
(8) 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withdrawn from the other edge by a bit of blotting paper.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: 
(f) The pyrenoids, small light-colored spots in the chlorophyll 
band, each surrounded by many dark-stained starch granules. 
(g) 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. 
Mount a few filaments of Spirogyra in water under a small cover- 
glass, 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 protoplast, 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 
