THE SORGHUMS 233 



212. Origin and crossing. — All three classes of sor- 

 ghums are thought to trace back to the same ancestor and 

 to be natives of tropical Africa. In some eastern countries, 

 the seeds of some of the sorghums are important human 

 foods. 



The various sorghums were introduced into the United 

 States in 1853, and at intervals throughout the next few 

 decades. 



Sorghums of all kinds freely cross with each other, the 

 hght pollen being spread by the wind. Therefore, varieties 

 from which seed is to be saved should not be planted 

 near any other varietj' or allowed to bloom at the same 

 time. 



213. Enemies. — In the Southern States, especially 

 from Louisiana eastward, the j'ield of seed from anj' class 

 of sorghum is quite uncertain, and complete failures to 

 mature seed are not infrecjuent. The usual cause of such 

 failures is the attack on the flowers and kernels by a minute 

 insect, the sorghum midge (Diplosis sorghicola). For this 

 no effective treatment is known. Probably some advan- 

 tage would result by planting this crop in fields remote 

 from where sorghum was grown the previous year. 



Sorghum kernel smut (Sphacelotheca sorghi) is a disease 

 caused by a fungus which destroys the individual grains. 

 It is easily prevented by either of the followdng methods: 



(1) by soaking the seed for planting for one hour in a solu- 

 tion of 1 ounce of formahn for each 2 gallons of water ; or 



(2) by scalding the planting seed for 10 to 12 minutes 

 in water kept at a temperature between 134° and 140° F. 

 Either of these treatments kills the germs of the disease 

 without injuring the seed. 



