PHYSIOLOGICAL TROUBLES 117 



the plant is growing. The control for this trouble usually 

 means the cleaning out of all diseased plants, withholding 

 the water supply, and providing for better ventilation. 



The cleaning up of the soil by steam sterilization or by the 

 treating of it with formalin is also effective in destroying 

 certain fungous diseases which are found in the soil. These 

 fungi oftentimes remain alive for a number of years and 

 attack the plants when they are planted. 



It is always advisable, therefore, to have the soil clean 

 and free from fungi. The plants should be grown where they 

 will have plenty of sunshine and have a good circulation of 

 fresh air so that the damp air will be blown away and never 

 allowed to collect about the seedlings. 



PHYSIOLOGICAL TROUBLES. 



Any serious disturbance in the life processes of the plant 

 which cannot be attributed to an organic factor, such as 

 insect, fungus or bacteria, is called a physiological trouble. 

 The peach yellows and the little peach are two common 

 examples of injury that are included under physiological 

 trouble. The most recent work on physiological troubles 

 seems to indicate that the plants are growing under unfavor- 

 able conditions, and that there is a lack of certain elements 

 in the soil which produces these troubles. In fact physio- 

 logical troubles are not well understood, although more 

 information is being gained every year and perhaps in the 

 near future more suggestions can be offered. 



Control Measures of Physiological Troubles. — No definite 

 remedial measures are at our disposal for the control of the 

 so-called physiological troubles. By that is meant that it is 

 of no avail to spray or to treat the plant with any solution 

 for the control of , this class of troubles. A physiological 

 trouble, as the term implies, is some interference with the 

 natural process of the growth of the plant, and is thought 

 to be the result of insufficient iron or some other element 

 in the soil. 



The only means of control, therefore, would be to supply 

 the material that is lacking, so the plant will develop normally. 



