CHAPTER XII. 



THE COLLECTION AND MOUNTING OF OBJECTS TEST- 

 FLUIDS. 



THERE is little need that I should say much on the 

 collection of objects you may wish to examine ; a 

 little experience will prove the best instructor. If 

 you wish to collect Desmidiacese and Diatomaceae, 

 you should take with you two or three wide-mouthed 

 bottles with corks, a tin scoop, a sharp hook for cut- 

 ting off stems of aquatic plants, which are often covered 

 with minute vegetable organisms (these two last should 

 be made to screw on to a long light bamboo rod), 

 and a lens. The Desmidiacese occur in slow-running 

 rivers, pools, ditches, especially those on boggy moors. 

 They often form a greenish cloud on the stems and 

 leaves of water-plants, or on the ground. They may 

 be taken up from the ground by the scoop, or from 

 the stems of plants by your fingers. If placed in 

 bottles and exposed to the light, these vegetable forms 

 will grow, and you may employ your time advan- 

 tageously in studying the development. Diatomaceae 

 are also found in profusion on the stems and leaves 

 of aquatic plants, presenting themselves as coloured 

 fringes, or forming a covering to stones or rocks in 

 cushion-like tufts, or spread over their surface as 

 delicate velvet, or depositing themselves as a filmy 

 stratum on the mud, or intermixed with the scum of 

 living or decayed vegetation on the surface of the 

 water. They are often mixed with sand and mud; 

 and the best way to get rid of these impurities is to 

 place the lot in a saucer of water, and expose it to the 

 light, when the diatoms may be skimmed from the 

 surface. Various beautiful forms occur upon sea* 



