64 THE AMERICAN MONTHLY [March, 



J. W. Stephenson finds a valuable resolving power in a solution of 

 phosphorus in bisulphide of carbon ; for the amateur it would be advis- 

 able not to play with so highly inflammable a solution. Prof. II. L. 

 Smith and Mr. W. C. Meates have devised media in which sulphur, 

 arsenic, and bromine are compounded, and although they give admir- 

 able mounts when first set up, after a time crystallization sets in and 

 spoils the slide. It will be as well to be content for the present with 

 balsam and Van Heurck's preparation. 



Associated with diatoms the collector will often find desmids These 

 may be distinguished from diatoms by their bright emerald-green color. 

 The desmidieaj are a family of fresh-water algte, and are among the 

 most beautiful objects either from their transparent green color or from 

 the great diversity of their form. Unlike the diatoms, the desmids grow 

 only in fresh water, and prefer a quiet pool in an open and exposed situa- 

 tion, and although they may be found in streams, it will be useless to seek 

 them unless the stream is a very slowly running one. Small shallow 

 pools in boggy ground are the most likely spots for them, and they may 

 be easily collected by the shallow spoon recommended for the collec- 

 tion of diatoms, if, like them, they are spread on the surface of a muddy 

 bottom. When they grow on the stems of aquatic plants, these may be 

 gathered bodily, and transferred to a glass bottle of water. If they are 

 scattered through the water, they may be collected by a small muslin 

 ring-net, to be described later on, and the net turned inside out in the 

 bottle of water, when the desmids will be washed oft', and if this is placed 

 in the sun-light on reaching home the desmids will be found by the 

 next morning congregated at that side of the bottle nearest the light, 

 and tolerably free from contamination. 



Mounting media for desmids which will preserve their beautiful 

 colors are still to be invented. There are only two which seem to act 

 fairl}^ well. Some add camphor water to that in which they have been 

 growing, when they may be mounted in it. This plan answers as well 

 as any and is to be preferred. Others employ a preservative solution : 

 Distilled water sixteen parts, alcohol one part, and a few drops of cre- 

 osote ; stir in a small quantity of chalk, and filter. Mix the liquid with 

 an equal part of camphor water, and before using make a cone of stout 

 blotting-paper the size of an ordinary thimble, and filter as much asje- 

 quired for one mounting on the slides, the desmids to be mounted hav- 

 ing been previously placed. A good preservative for these, and also 

 for delicate algte generally, is a solution of one part of acetate of alumina 

 to four parts of distilled water. With all these good mounting media 

 the color after a time disappears from the endochrome, and only the 

 outer form remains to tell the story. One species will always excite 

 interest, whether we regard its animal-like movements or the violent 

 vicissitudes through which it has to pass. It may often be found in the 

 metal gutters of buildings, where it is subjected to such extreme heat 

 that the hand brought incautiously in contact with the metal in the 

 height of summer is speedily withdrawn, or it may be found on the 

 Alpine snows in the depth of winter, where it is better known as "red 

 snow " than by itsbotanical name, Protococctis pluvialis. Thedried-up 

 powder in the metal gutter will often afford a crop when placed in water 

 and deposited near a window, when, in a day or two, that side of the 

 water near the light will be found swarming with pale green moving 



