236 COTTON CULTURE 



weather, and therefore an unfavorable condition for its development 

 is created by spacing the plants widely, so that the maximum 

 amount of sunshine will be admitted to the bolls. Certain varieties 

 of cotton are partially resistant to boll-rot and such may be used 

 to advantage in sections where the disease is widely prevalent. The 

 selection of the seed of uninfected plants is also recommended as 

 a means of checking fhe spread of this disease. 



Cotton Wilt. Cotton wilt comes from the soil. It is a thread- 

 like fungus growth, which enters the plant through the roots and 

 interferes with the upward passage of water to the stems. It may 

 attack the plant at any time after the leafing-out stage, but the 

 height of its virulence is reached after the bolls have formed. The 

 disease is indicated by a sudden wilting of the plants or by their 

 dwarfed appearance. In either case the plants may shed their 

 leaves and die, or may live in an unthrifty condition. 



Wilt can only be controlled by burning infested plants, and by 

 a rotation of crops through which cotton is kept from the land for 

 three or four years. 



Cotton Rust. The black rust of cotton is perhaps the most 

 destructive and widely distributed disease of the plant. It is a 

 fungous disease which causes the leaves to become yellow or black- 

 ened and to fall from the branches. The development and maturing 

 of the bolls is thus prevented and the crop is often seriously damaged. 



On light sandy soils, the use of 80 to 100 pounds of kainit, 

 which may be applied with other fertilizers, has been found a 

 remedy for black rust. Under this treatment the plant retains its 

 foliage until the bolls have matured. 



LABORATORY EXERCISES 



( 1 ) Remove the bracts and petals of a cotton flower and make a draw- 

 ing showing the stamens and stigmas. Why do cotton flowers so readily 

 cross-pollinate ? 



(2) Compare the bolls of a short-staple variety with those of a long- 

 staple variety. Make an outline drawing of a boll from each variety, 

 showing the difference in their form. Compare the number of bracts with 

 the number of cells, or compartments, in the boll. Are they equal? 



(3) Straighten from the seed the liber of a short-staple and of a long- 

 staple variety (see Figs. 80 and 81). Compare the length of the two 

 classes of fiber. Pull a few fibers of each class; twist those of each class 

 into a string and note their comparative breaking strength. 



(4) If microscopes are at hand, observe the three classes of fibers 

 unripe, half-ripe and ripe (see Fig. 82). Note the flattened twisted 

 form of the ripe fibers. Separate a few fibers of each class; twist each lot 

 into a string and compare their breaking strength. What are the desirable 

 qualities of the fiber? 



