Chlorophyceae 



167 



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 

 osrnic 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 



FIG. 33. Scenedesmus: photomicrograph from a preparation by Dr. Yama- 

 nouchi, mounted whole and stained as described in the text; Cramer contrast 

 plate; 4 mm. objective; ocular X4; yellowish-green filter; camera bellows, 1 

 meter; arc light; exposure, 6 seconds. X675. 



usual difficulty with this form, and with many others, is that the 

 background stains and so makes the mounts untidy. The following 

 method by Yamanouchi will produce beautiful preparations (Fig. 33) : 



1. Dry on the slide, 24 hours. 



2. 10 per cent alcohol over night to remove chlorophyll. 



3. Safranin (alcoholic), 4 days. 



4. Water, o minutes. 



5. Aqueous gentian- violet, 2 days. 



6. Water, a few seconds. 



7. Orange G, aqueous, 3 minutes. 



