314 GENERAL SCIENCE 



priving the limb of the food necessary for its growth, and causing 

 the twig to have a blackened, withered appearance. Leaves often 

 remain on such twigs during the winter time. The limb should be 

 cut off with a knife which has been dipped in a 5 per cent solution 

 of carbolic acid, and the places sealed with wax to prevent insects 

 and birds from carrying the disease from one tree to another. 



Black Knot. Black knot is one of the most serious known diseases 

 of trees. It is contagious. Large black knotty excrescences grow 

 on the limbs of trees. These should be cut off and burned as soon 

 as observed. The disease attacks plum and cherry trees especially. 



Fruit Mold. Cherry and peach trees are often seriously affected 

 by a brown rot which attacks the unripe fruit on the tree and turns it 

 soft and brown with a fuzzy coat of mildew. It is usually prevented 

 by spraying the tree several times with a self-boiling lime sulphur wash. 



Oat and Wheat Smut. On very young oat and wheat plants a 

 disease develops which causes the blackening of the heads of grain. 

 If such grain is threshed, this black part, consisting of the spores of 

 tiny fungus plants, is driven into the air. These spores will settle 

 on the seeds and, if planted, will cause the disease to thrive in the 

 next crop. If the seeds are soaked for a few minutes in a solution of 

 formaline, the bacteria will be killed. 



Potato Scab. Scabby potatoes are caused by the growth of 

 bacteria. Seed potatoes should be soaked in a f per cent solution 

 of formaline for two hours. 



Potato Blight. Another destructive disease of potatoes is caused 

 by a fungus which attacks the foliage of potato plants. Potato 

 fields must be sprayed in order to prevent the growth of this blight. 



Club Root. Club root is a disease of cauliflowers, turnips, cab- 

 bage, etc., which causes the appearance of large knotty bunches on 

 the roots. Eighty or ninety bushels of lime per acre prevent the 

 development of this disease. 



QUESTIONS 



1. Why must an attack of measles be considered serious? 



2. How may the germ be prevented from spreading? 



3. Why is it possible for people to get scarlet fever from 

 handling material in an attic? 



