190 GLAUCUS; OE, 



once more,* " thousands of tiny globules forming on 

 every plant, and even all over the stones, where the 

 infant vegetation is beginning to grow; and these 

 globules presently rise in rapid succession to the 

 surface all over the vessel, and this process goes on 

 uninterruptedly as long as the rays of the sun are 

 uninterrupted. 



" E"ow these globules consist of pire oxygen, given 

 out by the plants under the stimulus of light ; and 

 to this oxygen the animals in the tank owe their 

 life. The difference between the profusion of oxygen- 

 bubbles produced on a sunny day, and the paucity of 

 those seen on a dark cloudy day, or in a northern 

 aspect, is very marked." Choose, therefore, a south 

 or east window, but draw down the blind, or throw 

 a handkerchief over all if the heat become fierce. 

 The water should always feel cold to your hand, let 

 the temperature outside be what it may. 



IText, you must make up for evaporation by fresh 

 water (a very little will suf&ce), as often as in sum- 

 mer you find the water in your vase sink below its 

 * P. 259. 



