JET. 38.] LETTER TO HIS NIECE. 77 



been taken in the vain hope that her life might be 

 lengthened by residence in a southern climate. This 

 letter displays his attention to every detail of the 

 observations he counselled her to make, and his solici- 

 tude to cherish in the fading young life an unceasing 

 interest in the marvellous works of nature. In read- 

 ing between the lines we are conscious that a tender 

 sympathy is expressed : 



LONDON, 25th July 1850. 



MY DEAR SOPHIA, The plant in the bottle which I sent you 

 yesterday is a water-grass, in repute for the exhibition of the 

 circulation of the sap in vegetables. You will, I think, find 

 it a very interesting phenomenon. It is easily shown, and the 

 specimen can be preserved for any length of time in water. 

 You can plant it in some washed vegetable mould, an inch 

 thick, on the bottom of any open glass jar or vase filled up with 

 water. 



What I should recommend you to do would be to get any 

 common glass jar, about 8 to 12 inches high, and 4 to 8 inches 

 across ; place at the bottom of it about 1 or 1 J inch of washed 

 vegetable mould (washed, because it would otherwise make the 

 water too muddy), and then plant it with this and any other 

 water ground plants (mosses especially). Fill the jar to within 

 an inch of the top with dirty pond water (which will soon 

 become clear), and then put on the top of the water a few 

 floating water-plants such as duckweed and ranunculus. In- 

 troduce into the water any water-insects or fresh-water shells 

 and small Crustacea as the Planorbis, Lymnea, Helix, Cypris, 

 &c. The plants at the top will thus prevent evaporation, whilst 

 the animal and vegetable life will (as long as they are alive) 

 keep the water fresh and free from putrefaction. After a short 

 time the water will teem with a most active population, whose 

 habits and characters you can study at your leisure. The larger 

 animals will be visible enough through the glass, whilst the 

 smaller ones you can get out and place under the microscope 

 by means of a small dipping-tube. . . . Your mamma will, I 

 have no doubt, be able to assist you in all the manipulations, 



