Figure 111. A, In the protoplasm of young cotton fibers, disc-shaix,>d cellulose- 

 forming plastids, varying over a wide range in diameter, are barely visible. The 

 relative refractive indices of the plastids and of the cytoplasm in which they are float- 

 ing obscure their contents and cause them to resemble vacuoles (1000 X). B, Early 

 stage of fibril formation in the young cotton fiber (1320 X). C, Cellulose particles 

 and a cellulose ring in a plastid removed from a young cotton fiber (1650 X). D, Frag- 

 mentation of a cellulose ring, taken from a plastid, to form the cellulose particles 

 (1650 X). E, Cell membrane of the cotton fiber after the deposition of cellulose fibrils 

 in spiral arrangements (1254 X). 



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