TYPES OF CRYPTOGAMS; THALLOPHYTES 215 
THE STUDY OF SPIROGYRA 
279. Occurrence. 
as pond-scum, or “frog-spit,” occurs widely distributed throughout 
the country in ponds, springs, and clear streams. It is of a green 
or yellowish-green color, and in sunny weather usually floats on or 
near the surface of the water, buoyed up by the numerous oxygen 
bubbles which it sets free. It may be found flourishing in unfrozen 
springs, even in midwinter. 
271. Examination with the Magnifying Glass.1— Float a little of 
the material in a white plate, using just water enough to cover the 
bottom of the latter. Study with the magnifying glass and note the 
green color of the threads and their great length as compared with 
their thickness. Are all the filaments about equal to each other in 
diameter ? 
Handle a mass of the material and describe how it feels between 
the fingers. 
272. Examination with the Microscope. — Mount in water under 
a large cover-glass and examine first with a power of about 100 
diameters, then with a power of 200 diameters or more. Note the 
structure of the filaments. Of what is each made up? Are all the 
Spirogyra, one of the plants commonly known 
units alike? 
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 num- 
ber of bands is an important characteristic in distinguishing one 
species from another. 
Run in five-per-cent salt solution at one edge of the cover-glass 
(withdrawing water from the other edge with a bit of blotting 
paper). If any change in the appearance of the cell becomes evi- 
dent, make a sketch to show it. What has happened to the cell- 
contents? Explain the cause of the change by reference to what 
you know of osmose. 
1 Consult Huxley’s Biology and Spalding’s Introduction to Botany. 
