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GROWTH OF PLANTS 



acid. Farr and Eckerson ^^ published a similar result in 1934 under the 

 title "Separation of cellulose particles in membranes of cotton fibers by 

 treatment with hydrochloric acid" (Fig. 101). X-ray diagrams of these 

 preparations (Fig. 102) were pubhshed by Farr and Sisson ^^ during the 

 same year. The controlled treatment with hydrochloric acid had removed 



Figure 103. 1. Cell membranes of Spirogyra sp. show the presence of crystalline 

 material through their double refraction in polarized light (480 X). 2. Spiral fibrils in 

 the cell membrane of a cotton fiber {Gossypium hirsutum) in polarized hght (775 X). 

 3. Fibrils in the cell membrane of the cotton fiber are arranged parallel to the axis at 

 intervals throughout its length and produce "extinction areas" in polarized Ught 

 (775 X). 



