TYPES OF CRYPTOGAMS; THALLOPHYTES 241 
in nitric acid, the cellulose wall and its contents may be destroyed 
and the markings of the siliceous shell more easily observed. Each 
diatom consists of a single cell. 
272. Movements of Diatoms. — Living diatoms exhibit a peculiar 
power of movement. Jn the boat-shaped species the movement is 
much like that of a row-boat, forward or backward. 
THE STUDY OF SPIROGYRA 
273. Occurrence. — Spirogyra, one of the plants commonly known 
as pond-scum, or “frog-spit,” occurs widely distributed throughout 
the country in ponds, springs, 2 
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. 
274. Examination with the 
Magnifying Glass..— 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 thick- 
ness. 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. 
275, Examination with the Microscope. — Mount in water under 
a large cover-glass and examine first with a power of about 100 
Fic. 176.— A Group of Diatoms. 
A, Achnanthes; B, Cocconema; 
C, Meridion; D, Pleurosigma. 
1 Consult Huxley’s Biology and Spalding’s Introduction to Botany. 
