236 COTTON CULTURE 



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

 interferes witli 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 de- 

 structive and widely distributed disease of the plant. It is a fungous 

 disease which causes the leaves to become yellow or blackened 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. \Vliy 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 fiber 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? 



(5) Split a cotton seed and observe its simple structure. What are 

 the general parts of a cotton seed? 



(6) Compare, as to the proportion of opened bolls, a plant of an 

 early maturing variety with one of a late maturing variety. Observe, as 

 to structure and outline, the general difference between the two plants. 

 Why is an earlv maturing variety of cotton especially desirable? 



*The following practices are suggested to accompany this chapter. A 

 part or all of them may be included, according to convenience. 



