XVII 



FIBER CROPS 



COTTON 



Structure and Composition 



402. Relationships. Cotton fiber is derived from several 

 species of the genus Gossypium belonging to the mallow family 

 (Malvaceae}. Okra (Hibiscus esculentus L.) and hollyhock 

 (Althaea rosea Cav.) belong to the same family. The species 

 of the genus Gossypium may be herbaceous, shrubby, or tree- 

 like, and are all probably under natural conditions perennial. 

 A characteristic of this genus is the black spots or glands on 

 nearly all parts of the plant. The principally cultivated species, 

 upland or short staple cotton (G. hirsutum L.), is herbaceous 

 and under cultivation an annual. The discussion which follows 

 relates to this species when not otherwise stated. 



403. Roots. While normally the cotton plant has a strong, 

 branching tap root penetrating deeply, the root system is sub- 

 ject to much modification, due to the nature of the soil and the 

 sub-soil. In some instances the tap root may be absent. At 

 the South Carolina Station well-developed tap roots were traced 

 in sandy soil and sub-soil to a depth of two to three feet with- 

 out coming to their end. On heavy clay loam only one plant 

 out of twenty had a well-developed tap root over nine inches 

 long. In either kind of soil the lateral roots began about three 

 inches below the surface of the soil and spread out in all direc- 

 tions, most of them being within nine inches of the surface, 

 although some of them bent down abruptly, penetrating as far 



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