448 THE STRUCTURE OF ECONOMIC PLANTS 



"3. Frequently the pattern of spirals first appearing in the secondary 

 wall is not similar to that in subsequent layers of the wall. Most of 

 the layers of the wall, however, follow a pattern that is established 

 soon after secondary thickening has begun." 



The strength of a fiber is dependent primarily upon the thickness 

 of the cell wall, and not necessarily upon the diameter of the cell 

 since some large fibers may have relatively thin walls. Strength 

 and length are greatly affected by variations in the environmental 

 factors, as well as by the genetic constitution of the strain of cotton 

 grown. Fineness in quality is conditioned upon the diameter of 

 the fibers together with the thickness of their walls; and the silky 

 texture of Sea Island cotton is related in part to the fact that it has 

 fibers of a somewhat smaller caliber than a variety such as the 

 Indian wool cotton. Color and luster may be associated to some 

 extent with cultivation and selection, the majority of wild cottons 

 being brownish in shade, while the cultivated varieties tend to be 

 white, cream-colored, or less frequently brown. The luster of the 

 l.r.t seems to be associated with the reflection of light from the 

 cutinized surface of the hair; but according to Balls (4), it also 

 results from the translucence of the fibers and the refraction of a 

 certain proportion of the light in addition to its reflection from the 

 concave surfaces within the fiber. 



LITERATURE CITED 



Anderson, D. B., and Kerr, T., "Growth and structure of cotton fiber." 



Itjd. and Eng. Chem. ^0: 48-54, 1938. 

 , and MooRE, J. H., 'The influence of constant light and temperature 



upon the structure of the walls of cotton fibers and collenchymatous cells."' 



Am. Jour. Bot. 24: 503-507, 1937. 

 Balls, W. L., "The sexuality of cotton." Year Book, Khed. Agr. Sac, Cairo, 



1905. 

 , The Development and Properties of Raw Cotton, A. & C. Black Ltd., 



London, 1915. 

 , "The existence of daily growth rings in the cell walls of cotton hairs." 



Proc. Roy. Soc. B. qo: 541-554, 1919. 



_, The Cotton Plant in Egypt, The Macmillan Co., 1919. 



Barritt, N. W., "The structure of the seed coat of Gossypium and its relation 

 to growth and nutrition of the lint." Ann. Bot. 43: 482.-489, 192.9. 



Beal, J. M., "A study of the heterotypic prophases in the microsporogenesis 

 of cotton." La Cellule, }8: 147-168,192.8. 



Brown, H. B., Cotton, McGraw-Hill Book Co., 192.7. 



