DROPSY OF TOMATO. 179 



of needed light. By a process known as transpiration, 

 plants are relieved of much water when well lighted, 

 but in poor light, since the roots are absorbing water, it 

 is apt to accumulate to excess. Well lighted parts of the 

 house, then, should be selected for the tomatoes. 



" 2. Too much water in the soil. Water in excess can 

 be withheld from the soil and prevent the trouble, and yet 

 provide enough for the plants to grow. 



"3. The temperature of the soil may be too near that 

 of the air. A high temperature of the soil makes the 

 roots active, and if the temperature of the air is not con- 

 siderably higher an excess of water is apt to accumulate 

 in the plant. The aim would be, then, to have the tem- 

 perature of the air considerably higher than that of the 

 roots. 



" Lack of proper light also brings about the following 

 harmful conditions : 



"i. Acids in the plant accumulate in the dark, and in 

 strong light they decrease. When there is an abundance 

 of water in the plant these acids draw large quantities 

 into the cells, causing the cells to swell, resulting many 

 times in oedema, or in the killing of the protoplasm, so 

 that these parts of the plant die and become brown or 

 black. 



" 2. Lack of light causes weak cell walls. It is only 

 when well lighted that plants are capable of making sub- 

 stances to build up cell walls with. Therefore, lack of 

 light not only favors the accumulation of water, if other 

 things are favorable, but it prevents the plants from build- 

 ing up strong tissues. In such cases plants can grow 

 themselves to death. Possibly artificial light might be 

 used to advantage. 



"A quiet and close atmosphere also favors the ac- 

 cumulation of water in the plant. Good ventilation 

 should then be secured. Some means for the artificial 

 agitation or exchange of the air at night might probably 

 be profitably devised. 

 13 FORC. 



