216 



CIVIC BIOLOGY 



late blight, or rot, and dry rot, or stem blight, of potato ; and crown gall 

 of grapes, berry bushes, and fruit trees. So, too, pear and apple blight 

 have often been scattered broadcast from nurseries because disinfec- 

 tion of pruning tools was neglected. In general, disease shows up 

 clearly in the nursery or field, while it would require bacteriological 

 and microscopic methods to find the germs within the seeds or stocks. 

 Go out and hunt over local nurseries or seed farms. Ask experts from 

 them to come in and demonstrate and discuss their methods. All who 



FIG. 103. Corn smut (Ustilago zece) 



propose to distribute these important supplies to the public ought to 

 know their business by this time. The best firms employ trained ex- 

 perts to see : to it that stock is free from disease, and then they may 

 send it to branch farms, far away from any possible contamination, to 

 have it propagated for the market. 



"2. If spores are alive on the seeds or tubers, ready to attack the 

 embryo plant when it germinates, kill them before planting. 



Scab of potatoes and smuts of grains are examples. Soak seed potatoes 

 for two hours in formalin solution (1 ounce to 2 gallons of water) or in 

 mercuric chloride (corrosive sublimate) solution (1 ounce to 8 gallons of 

 water). External spores of the smuts on wheat, oats, and barley are 

 killed by soaking for from ten to twenty minutes in formalin solution 

 (1 pint to 30 gallons of water) or by warming up the seed in water at 

 110-120 and then holding it for ten minutes in water at 132-133 F. 



