CHLOROPHYCEAE 
187 
or cell wall, thus allowing an unobstructed view of the figures. 
While figures occur occasionally in the daytime, collect your material 
at night, preferably near midnight. 
Spirogyra is easily imbedded and cut. 
Scenedesmus. —Scenedesmus (Fig. 40) is found everywhere as a 
constituent of the fresh-water plankton. It is more abundant in 
stagnant water. It often appears in considerable quantity in 
laboratory cultures, where it may be kept for years in a tightly closed 
glass jar without renewing the water, the lid being removed only 
when material is needed. 
The form is so small that in living material little more than the 
general form can be distinguished. Excellent mounts are easily and 
quickly made. Smear a very thin layer of albumen fixative upon the 
slide, and add a drop of water containing the Scenedesmus. The 
drop may be inverted for 1 or 2 minutes over the fumes of 1 per cent 
osmic acid. No washing is necessary, and good mounts may be 
made without any fixing whatever. Allow the drop to dry com¬ 
pletely. It is better to leave it for 24 hours before proceeding. The 
usual difficulty with this form, and with many others, is that the 
background stains and so makes the mounts untidy. The follow¬ 
ing method by Yamanouchi will produce beautiful preparations 
(Fig. 40): 
1. Dry on the slide, 24 hours. 
2. 10 per cent alcohol over night to remove chlorophyll. 
3. Safranin (alcoholic), 4 days. 
4. Water, 5 minutes. 
5. Aqueous gentian-violet, 2 days. 
6. Water, a few seconds. 
7. Orange G, aqueous, 3 minutes. 
8. 95 per cent alcohol, a few seconds. 
9. Absolute alcohol, 1 minute. 
10. Clove oil, until the stain is satisfactory. Different collections of 
Scenedesmus stain very differently, but the time in clove oil is likely 
to be long, even as long as 6 hours. 
11. Xylol, 5 minutes. 
12. Mount in balsam. 
Hydrodictyon.—-This is popularly known as the “water-net.” 
Hydrodictyon is found floating or suspended in ponds, lakes, or slow 
streams. The young nets are formed within the segments of the 
