the cells, particularly of the palisade tissue, or 

 hasten the physiological process. This activity 

 calls at once for large supplies of water, and it is 

 drawn first from the overlying epidermal cells; 

 these cells being emptied of their contents, collapse 

 like an empty grain bag. In other words, the vital 

 activity is hastened so much by the naked light 

 that the plant cannot supply materials quickly 

 enough, and it is forced to death." 



Plain glass will strain out these dangerous ultra- 

 violet rays sufficiently to prevent this damage, or 

 it may be avoided by removing the lamp to a suffi- 

 cient distance from the plants. 



Experiments are being conducted which may de- 

 termine for us just what colors of lamp-shades are 

 the most desirable for use in cultivating the various 

 plants which are benefited by the arc-light. Ex- 

 periments have been made with the spectrum of the 

 sun to find out which of its rays are efficacious in 

 causing the formation of woody fibre, which in the 

 formation of starch, which in the formation of 

 chlorophyll, etc., but the results have not been 

 conclusive on account of the difficulty of maintain- 

 ing the spectrum steadily at the same place, and on 

 account of the short periods of time it could be 

 depended upon for action. But with the arc-light 

 the spectrum can be furnished continuously, and 

 its different colors kept upon a number of similar 

 plants as long as desired. Thus we may learn 

 which colors are best suited to the varying needs 

 of plants at the different stages of their growth. 

 Here again we may meet the question of dosage, 



