242 FOUNDATIONS OF BOTANY 
diameters, then with a power of 200 diameters or more. Note the 
structure of the filaments. Of what is each made up? Compare 
with the structure of Oscillatoria. 
Move the slide so as to trace the whole length of several filaments, 
and, if the unbroken end of one can be found, study and sketch it. 
Study with the higher power a single 
cell of one of the larger filaments and 
ascertain the details of structure. Try 
to discover, by focusing, the exact shape 
of the cell. How do you know that 
the cells are not flat? Count the bands 
of chlorophyll. The number of bands 
is an important characteristic in dis- 
tinguishing one species from another. 
Run in five-per-cent salt solution at 
one edge of the cover-glass (withdraw- 
ing water from the other edge with a 
bit of blotting paper). If any change 
in the appearance of the cell becomes 
evident, make a sketch to show it. 
What has happened to the cell-con- 
_ tents? Explain the cause of the 
Fic. 177.— Process of Cell-Multi- 
plication in a Species of Pond- Change by reference to what you know 
Scum. (Considerably magnified.) of osmose. 
A, portion of a filament partly On a freshly mounted slide run 
ates a ey ibaa 95 pid under the cover-glass iodine solution, 
completed, a new partition of a little at a time, and note its action 
ieee meats petals Re “4 on the nucleus. Is any starch shown 
fied, bee eaten scene to be present? If so, just how is it 
d, general cell-wall c, and a_ distributed through the cell? 
i. aoe re 276. Reproduction of Spirogyra. — 
The reproductive process in Spirogyra 
is of two kinds, the simplest being a process of jission, or cell- 
division. The nucleus undergoes a very complicated series of 
transformations, which result in the division of the protoplasmic 
contents of a cell into two independent portions, each of which is 
at length surrounded by a complete cell-wall of its own. In Fig. 176 
