156 GLAUCUS ; OR, 



more,* " thousands of tiny globules foi-ming 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 pro- 

 cess goes on uninterruptedly as long as the rays 

 of the sun are uninterrupted. 



" Now these globules consist of pure 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. 



Next, you must make up for evaporation by 

 fresh water. A very little will suffice, as often as 

 in summer you find the water in your vase sink 

 below its original level, and prevent the water 

 from getting too salt. For the salts, remember, 

 do not evaporate with the water, and if you left 



* P. 259. 



