288 CORN CROPS 



crossing takes place. Many writers have stated that 

 such cross-pollination occurs also at very long distances, 

 but this seems to be less conclusively proved. Probably 

 a distance 'of 8 to 10 rods to leeward is the maximum at 

 which appreciable hybridization occurs." Ball also states 

 that the pollen is mostly shed during the early morning 

 hours, when the winds are usually at lower velocities 

 than later in the day. 



Crossing of types. — All the different types of sorghum, 

 as sweet sorghums, non-saccharine types, and broom-corns, 

 cross readily. (See Fig. 115.) Broom-corn growers must 

 exercise some care in keeping their seed stocks pure, in 

 regions where other varieties of sorghum are grown. 



CLIMATE AND SOILS 



217. The entire botanical genus {Andro-pogon) , made up 

 of hundreds of species, is found growing principally in 

 wide-open plains regions. HackeP states, "the species 

 prefer dry places, especially savannas." 



Climatic requirements 



Temperature and sunshine. — Sorghum, like corn, is a 

 plant of tropical origin, varieties of which have been 

 adapted to temperate climates. Like corn, it requires 

 abundant sunshine and warm weather, being very sensitive 

 to cool nights. At high elevations where nights are gen- 

 erallj^ cool, sorghum seldom does well even when the days 

 are warm and sunshiny. 



Humidity and rainfall. — While both corn and sorghum 

 require sunshine and warmth, they apparently differ 

 somewhat as to humidity, corn preferring regions of high 



1 Hackel, Edwakd. The True Grasses, p. 57. 



