Propagation and Care of Plants 



FIG. 65. Oil heaters in use in an orchard. 



r. stilling 



W. T. Skilling 



FIG. 66. One morning, at daybreak, the Fahrenheit thermometer registered 

 39 degrees above zero on top of this bridge, and there was, of course, no frost 

 at that level ; but in the valley below the thermometer registered 29 degrees, 

 and there was a heavy frost. 



