MANUAL OF GENEEAL AGRICULTURE. 83 



ance of the water. Can you make out the individual 

 plants? This power of your microscope magnifies 50 

 times. Selecting a thin place in the mount turn on the 

 high power and observe : 



8. The very small, short rod-shaped bacteria ( magni- 

 fied about 500 times.) 



9. In many cases longer rods made up of 2 or more 

 plants fastened. Each plant is a single bacterium. They 

 multiply by the simple division of each plant into two. 

 They may reach their full growth in less than half an 

 hour. Draw. 



Make mounts on clean slides from differently appear- 

 ing colonies. Compare the bacteria from these different 

 colonies as to form, size, etc. Do they seem to be all alike ? 

 Are all the bacteria in any given colony alike? (Do not 

 use the same slide more than once without thorough wash- 

 ing and clean your needle each time before making a 

 transfer). Are the bacteria from different appearing colo- 

 nies always different in form, size, motility, etc. ? 



PART V ENEMIES OF CROPS. 

 67. APPLE SCAB. 



Of all diseases of the apple, this is the commonest and 

 best known to the growers. It is the one fungus disease 

 for which they spray. It is world wide, occurring prac- 

 tically wherever the apple is grown. While there is a 

 marked difference in the susceptibility of varieties, all will 

 sufor some under conditions especially favorable to the 

 fungus causing the disease. The scab of the pear is very 

 similar in its symptoms to that of the apple, but is 

 caused by a distinctly different species of fungus, which, 

 however, is closely related to the apple scab fungus. In 

 either case the remedy is the same. 



THE DISEASE. 



SYMPTOMS. The disease affects the leaves, flowers, 

 fruit and rarely the twigs. It lives over winter on fallen 

 leaves. 



