178 BREEDING CROP PLANT* 



which are resistant to wilt. A number of resistant high-yielding 

 varieties have been introduced in the cotton growing regions of 

 the United States. The character of wilt resistance was trans- 

 mitted in crosses but nearly every cross gave a different result. 

 In general, resistance proved dominant but there was often con- 

 siderable variability, possibly due to the gametic composition 

 of the parents or to the nature of the reaction between the disease 

 organism and the host plant or to the lack of uniform evironmental 

 conditions. Wilt resistance does occur and varieties may be 

 obtained which are resistant and are also of good quality with 

 respect to yield and staple. 



SORGHUM 



Origin. The numerous diversified forms of sorghum indicate 

 that it has been cultivated a long time. Evidence has been found 

 that it was grown in Egypt as early as 2200 B.C. Hackel places 

 all the cultivated sorghums and the various forms of Johnson 

 grass in one botanical species. It has been pointed out by Piper 

 (1916) that two species exist the perennials, Johnson grass and 

 its varieties (Andropogon halepensis), and the annual sorghums 

 (Andropogon sorghum). The former possesses rootstocks, and 

 it is difficult to cross it with either the cultivated or wild forms of 

 sorghum. 



The wild annual sorghums, which are found almost exclusively 

 in Africa, cross readily with the cultivated forms. Africa is 

 thought to be the native home of our cultivated sorghums. 



Classification and Inheritance. On the basis of the three 

 economic characters production of grain, sugar, and broom- 

 straw three distinct types of sorghums have been developed. 

 All of these produce forage and some of them, as Sudan 

 grass, are grown primarily for this purpose. Piper, after Ball, has 

 suggested a group classification for all the forms of A. sorghum, 

 cultivated in America, to which the student is referred (Piper, 

 1916). Only a brief statement will be given here. Small- 

 stemmed sorghums, such as Sudan-grass and Tunis-grass, 

 comprise one group. The other group, the large-stemmed sor- 

 ghums, are divided on the basis of the character of the pith 

 whether it is juicy or dry. The juicy sorghums may be either 

 sweet or slightly sweet to sub-acid. The dry sorghums are fur- 

 ther classified into varieties on the basis of panicle char- 

 acteristics. Hilson (1916) found that a pithy stalk was dominant 



