PLANT CELL MEMBRANES 283 



(8) The process of cellulose formation in living protoplasm was first 

 observed in Halicystis. The mechanism involved is one of successive cellu- 

 lose ring formation in the green chloroplasts, followed by ring fragmentation 

 to form the cellulose particles. 



(9) Cellulose formation by a similar method was later observed in color- 

 less plastids of the cotton fiber and in cells of the leaf and stem tissues of 

 the cotton plant. In the latter cells starch and cellulose are formed simul- 

 taneously in chloroplasts and colorless plastids respectively. 



(10) A conspicuous variation in the process of cellulose formation in 

 the chloroplast of Valonia consists in the formation of one closed cellulose 

 ring followed by the formation of a coiled cellulose fibril. 



(11) All mature cell membranes containing cellulose particles in various 

 proportions and types of arrangement were found to contain non-cellulosic 

 materials of various types and in different proportions. These combina- 

 tions of crystalline and non-crystalline components in intimate colloidal 

 association constitute a basis for understanding the relative properties of 

 the membranes of highly differentiated fibrous cells, such as cotton and 

 ramie, as well as those of the more primitive bladder-like cells, Halicystis 

 and Valonia. Considerations of the function of non-cellulosic materials in 

 controlling the phenomena of plasticity and deformability during the period 

 of cell enlargement, and the function of cellulose in establishing strength and 

 rigidity in the process of cell differentiation, constitute a new analytical 

 approach to the study of these two aspects of plant growth. 



Literature Cited 



1. Astbiiry, W. T., T. C. Marwick, and J. D. Bernal, "X-ray analysis of the structure 



of the wall of Valonia ventricosa," Proc. Roy. Soc. [Land.], B109 : 443-450 (1932). 



2. Barrows, F. L., "Cellulose membranes from various parts of the plant kingdom," 



C. B. T. L, 11(1939) : 61-82 (1940). 



3. , "Lamellate structure of cellulose membranes in cotton fibers," C. B. T. /., 



11 : 161-179 (1940). 



4. Compton, J., "On the behavior of plant fibers dispersed in cuprammonium hydroxide 



solution," C. B. T. I., 10 : 57-70 (1938). 



5. , "Structural relation of rayon to natural collulosic fibers. Study of the viscose 



process," Ind. Eng. Chem., 31 : 1250-1259 (1939). 



6. Farr, C. H., "Cytokinesis in the pollen-mother-cells of certain dicotyledons," 



Mem. New York Bot. Gard., 6 : 253-317 (1916). 



7. , "Root hairs and growth," Quart. Rev. Biol, 3 : 343-376 (1928). 



8. Farr, W. K., "Cell-division of the pollen-mother-cell of Coboea scandens alba," Bull. 



Torrey Bot. Club, 47 : 325-338 (1920). 



9. , "Studies on the growth of root hairs in solutions. The pH molar-rate relation 



for Brassica oleracea in calcium sulphate," Proc. Nat. Acad. Set., 15 : 464-470 

 (1929). 



10. , "Cotton fibers. I. Origin and early stages of elongation," C. B. T. I., 3 : 441- 



458 (1931). 



11. , "Cotton fibers. III. Cell divisions in the epidermal layer of the ovule sub- 

 sequent to fertiUzation," C. B. T. I., 5 : 167-172 (1933). 



