B. P. I.— 678. 



ARRANGEMENT OF PARTS IN THE COTTON 



PLANT. 



INTRODUCTION. 



The basis of all scientific study of cotton, as of other agricultural 

 plants, is the recognition and comparison of differences. Whether 

 experiments are being made for the breeding of better varieties or to 

 determine the most favorable conditions or methods of culture, 

 account must first be taken of the differences that are shown in the 

 characters and behavior of the plants. The scientific interest and 

 practical value of the results must depend very largely upon the 

 ability of the experimenter to recognize such differences and to under- 

 stand their relation to the development of varieties and to cultural 

 problems. 



Two principal kinds or classes of differences may be recognized in 

 the study of such a plant as cotton. The component parts, such as 

 the joints, leaves, flowers, or fruits, may differ, or there may be dif- 

 ferences in the number and arrangement of parts that are otherwise 

 alike. The body of the plant may be looked upon as a compound 

 structure or colony built of several kinds of structural units, com- 

 monly called joints or internodes. Changes of behavior that are of 

 serious economic importance may be brought about by changing the 

 number and arrangement of the parts of the plants, even without 

 altering the characteristics of the leaves, flowers, or other component 

 units of structure. 



Not only do the parts of an individual plant stand in relation to 

 other parts of the same plant, but all the individuals of a pure strain 

 or variety have the same system of arrangement of parts, though 

 variously modified under different conditions of growth. The leaves 

 and branches have definite positions on the stems, and the parts of 

 the flowers and fruits have characteristic numbers and places, in addi- 

 tion to their peculiarities of form and color. Hybrids, mutations, 

 and reversions usually show differences in arrangement of parts as 

 well as in other characters. Differences in arrangement are often the 

 most obvious and assist the breeder in recognizing the superior indi- 

 viduals and rejecting the inferior. 



96654°— Bui. 222—11 2 7 



