SUBSEQUENT CARE OF THE PLANT 175 



outsule. There is no external growth of a fungus, and rarely any 

 well defined small spots on the leaves. Fig. 72 shows the spots of 

 a fungous disease ; if this leaf had been attacked by a bacterial 

 or physiological disease, the entire leaf would probably have 

 shown signs of failing, for the food supply is usually cut off in 

 the leaf-stalk or the main veins. In Fig. 72, however, each spot 

 represents a distinct attack of the fungus. 

 Fig. 73 is a type of physiologial trouble, the 

 edge of the leaf dying from the cutting-off of 

 its food supply ; this dead border will widen 

 until the leaf dies. 



294a. Physicians treat some diseases by 

 prophylaxis, that is, by giving attention to 

 means of sanitation and of preventing the 

 spread of the disorder. Farmers must do the 

 same. Wire-worms are rarely troublesome Fig. 70. The tarnished 

 in short and quick rotations, particularly in plant-bug,-a sucking 



, . . insect, 



those in which sod is not a prominent fea- 

 ture. Club-root of the cabbage is rarely 

 troublesome on land which has not grown 

 cabbages or allied plants for a few years. 

 Apple-scab is least serious in those orchards Pig. 71. The strawberry 

 which have been thoroughly sprayed in pre- weevil, a chewing 

 vious years. Plum-rot is least troublesome > ns ect. 

 when the fruit is well thinned. Rose-bugs seldom trouble vine- 

 yards which are on strong or heavy lands. 



296a. Kerosene emulsion may be made as follows: Hard, 

 soft or whale-oil soap, ^ Ib. ; water, 1 gal.; kerosene, 2 gals. 

 Dissolve the soap in hot water; remove from the fire and while 

 still hot add the kerosene. Pump the liquid back into itself 

 for five or ten minutes or until it becomes a creamy mass. If 

 properly made, the oil will not separate out on cooling. For use 

 on dormant trees, dilute with from 5 to 7 parts of water. For 

 killing plant-lice on foliage, dilute with 10 to 15 parts water. 



Crude oil emulsion is made in the same way by substituting 

 rude oil in place of kerosene. 



