228 



THE FORAGE AND FIBER CROPS IN AMERICA 



purpose. The entire life cycle varies according to season and locality, more 

 particularly the temperature of the storeroom, from 21 to 80 clays. Chittenden 

 estimates six generations in a latitude such as the District of Columbia, with 

 a less number farther north. Insects may be destroyed in the infested seeds 

 without injury to the germinating power by fumigating with bisulphide of 

 carbon at the rate of one ounce to every hundred pounds of beans; or by 

 heating to a temperature of 145 F.; or by soaking seed for one minute in 

 boiling water. Badly injured seed will float in water, and may be removed and 

 destroyed. No other efficient means of preventing a field from being attacked 

 has been found. 



272. Threshing. A special type of thresher is required for 

 threshing beans and peas. When the bean pods are thoroughly 



Sectional view of bean thresher. Note the two cylinders 



dry, the seeds are readily separated from the pods, and are 

 easily split. When damp, the seeds are separated from the 

 pods with difficulty, and the seeds are less easily split. If the 

 pods in a load of beans were all of equal dryness, they could 

 be threshed fairly well by speeding the cylinder of the 

 thresher to suit the state of dryness; but if, as usually happens, 

 the pods vary as to dryness, no speed of the cylinder will be 

 best for all. If the speed is too high, some will be split; if too 

 low, not all the beans will be obtained. This difficulty is met 

 in bean threshers and pea hullers by having two cylinders run 

 at different rates of speed. The beans are run through a cyl- 

 inder at low speed, which threshes out the dry pods, the seeds 

 of which are thoroughly screened out before the partly threshed 

 material comes to the second cylinder run at a higher rate of 



