AN EVENING AT THE MICROSCOPE. 181 



The one-inch objective has given us a magnification 

 of about fifty, but now let us turn the nosepiece 

 round and bring the quarter-inch lens into position. 

 This is a glass constructed by the eminent opticians, 

 Messrs. Powell & Lealand, and it will give a 

 magnification of over three hundred linear with 

 -the B eyepiece of Ross. 



The first of these microscopic plants to which I 

 shall draw attention is a Desmid. Here is one, of 

 which an illustration is given (Fig. 44), called 

 Closterium. It is a familiar object, but in this case 



FIG. 44. Closteriwm striolatwm. 



familiarity does not breed contempt. Being of a 

 bright green colour and full of chlorophyll, which 

 requires the action of sunlight, it follows that the 

 proper time for collecting desmids is during summer 

 and autumn, and they are generally found near the 

 surface of the water, where the sun can get at them. 

 These pretty little plants lie almost at the very 

 bottom of the botanical scale. They belong to the 

 natural order Algce, of which seaweeds are the best 

 known types. But they are one-celled Algae and as 

 individuals are invisible to the naked eye. They are 

 exclusively fresh-water organisms, and are never 

 found in the sea. In this they differ from their 



