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contain chlorophyll or other pigments they are called chloroplasts or chromo- 

 plasts ; if they are colorless, they are called leucoplasts. For almost a century 

 microscopists have been able to observe the formation of starch in the plastids 

 of living cells and have found it to be one of the most common and most 

 conspicuous constituents of living protoplasm. 



Cellulose has been more elusive and its microscopic identification in the 

 living protoplast, long delayed. Until recently it was not known to exist 

 as a crystalline entity in the living cell before it made its appearance in the 

 cell wall. In 1934 cellulose crystallites in the form of barely visible, ellipsoid 

 particles [(1.1 x 1.5 microns) or (0.00004 x 0.00006 inch)] were observed 

 and identified in the protoplasm of many types of cells from various parts of 

 the plant kingdom. Subsequent studies in which microscopic, chemical, and 

 X-ray diffraction techniques have been used have confirmed and extended 

 these observations. 



The accumulated data have furnished no clew, however, to the place of 

 origin of the cellulose particles in the living protoplast. Within recent months 

 we have turned our efforts in this connection toward a more careful study 

 of the protoplasmic constituents of some of the large single-celled, marine 

 algae. The first observations which we have to report have been made upon 

 the green alga, Halicystis, obtained from Bermuda through the courtesy of 

 Doctor J. F. G. Wheeler of the Bermuda Biological Station for Research. 



In the young, disc-shaped chloroplasts of these large cells there are two 

 small, ring-shaped structures, usually placed so that an imaginary line pass- 

 ing through the central axis of each ring would lie approximately parallel 

 to the major axis of the plastid disc. As the chloroplast enlarges there is a 

 successive formation of new rings of larger diameter but equal thickness 

 immediately inside the plastid membrane. These larger rings disintegrate 

 within the plastid into uniform-sized particles. After the formation and 

 particulate disintegration of two or more large rings, the chloroplast mem- 

 brane itself breaks down, releasing into the outer regions of the cytoplasm, 

 the entire plastid content. This material of plastid origin goes directly into 

 the formation of the lamellae of the cell membrane. The two small rings 

 disintegrate, each into four particles, either before the breakdown of the 

 plastid membrane, after the breakdown of the plastid membrane, or after 

 the deposition of the plastid material in the cell membrane. THESE 

 UNIFORM-SIZED PARTICLES RESULTING FROM THE DISINTE- 

 GRATION OF THE RINGS FORMED WITHIN THE CHLORO- 

 PLAST WE HAVE IDENTIFIED AS MERCERIZED CELLULOSE 

 BY BOTH MICROSCOPIC AND X-RAY DIFFRACTION AN- 

 ALYSES. 



"Mercerized" cellulose was first produced by John Mercer in 1844 through 

 the treatment of the "native" cellulose of cotton fibers with solutions of strong 

 sodium hydroxide. Cellulose particles mercerized by this method can be dis- 

 tinguished from native cellulose particles by their blue coloration in solutions 

 of iodine (I2KI) without previous treatment with strong acid, and by their 

 characteristic X-ray diffraction pattern. Doctor van Iterson of Delft observed 

 in 1936 that the cell membrane of Halicystis turns blue when treated with 



