95 



iodine solutions and questioned, therefore, the cellulose nature of the crystal- 

 line membrane material which is clearly doubly-refractive in polarized light. 

 Doctor Sisson of our department found in 1938 that the X-ray diffraction 

 pattern of the cell membrane of Halicystis showed the presence of mercerized 

 cellulose and the absence of native cellulose. This represented the first recorded 

 observation of the presence of mercerized cellulose in an untreated plant 

 cell membrane and explained the color reaction of the membrane in iodine 

 solutions. There is, therefore, this limited but important background of ac- 

 cumulated facts with which to correlate our present data and assist in con- 

 firming our conclusion that MERCERIZED CELLULOSE PARTICLES 

 ARE FORMED IN THE LIVING CHLOROPLAST OF HALICYSTIS 

 AND THAT THEY, WITH THEIR ASSOCIATED MATERIAL OF 

 PLASTED ORIGIN, GO DIRECTLY INTO THE FORMATION OF 

 THE LAMELLAE OF THE CELL MEMBRANE. 



The question at once arises as to whether or not the process of formation 

 of cellulose particles within plastid-like structures in plant cells is restricted 

 to mercerized particles in chlorophyll-containing plastids. These questions 

 have been answered by a reinvestigation of the protoplasm of the developing 

 cotton fiber. Our previous study of the young cotton fiber had dealt only 

 with the identification of cellulose particles scattered separately in the cyto- 

 plasm and their behavior during fibril formation and subsequent deposition 

 in the membrane. We now find in the cytoplasm, in corresponding stages of 

 fiber development, structures which are circular in outline, variable in size, 

 colorless, and so close in their refractive index to the cytoplasm itself that 

 they are very nearly invisible. After removal of these structures from the 

 fibers under carefully controlled osmotic conditions, their contents are more 

 clearly visible. THE FORMATION OF "NATIVE" CELLULOSE PAR- 

 TICLES IN THE COLORLESS PLASTID-LIKE STRUCTURE OF 

 THE COTTON FIBER BY A PROCESS OF RING-FORMATION 

 SIMILAR TO THAT OF MERCERIZED PARTICLE FORMATION 

 IN HALICYSTIS CAN THEN BE OBSERVED. 



The formation of mercerized cellulose particles in the chloroplast of 

 Halicystis and of native cellulose particles in the colorless plastid of the 

 cotton fiber takes place, therefore, by structural processes which are visible 

 and essentially similar. In each instance the concentric rings of varying 

 diameter but equal thickness make possible, through ring disintegration, the 

 formation of cellulose particles of characteristic uniformity in size. This 

 process of cellulose particle formation has no morphological similarity to the 

 well-known appearance of starch grain formation in either chloroplasts or 

 leucoplasts. Upon the basis of these observations THE EXISTENCE OF 

 CELLULOSE-FORMING PLASTIDS IS THEREFORE DEFINITELY 

 ESTABLISHED. 



The knowledge that fully formed cellulose particles are discharged into 

 the cytoplasm by the rupture of the membrane of the plastid in which they 

 have been formed serves to clear away the mystery of the sudden appearance 

 of crystalline cellulose particles in living cells. The fact that cellulose particles 

 can be formed in either a chloroplast or a colorless plastid, and in either the 



