PLANT CELL MEMBRANES 265 



stages of development of the single fibrils could be observed. Each fibril 

 was formed by the arrangement, in single rows, of the diminutive cellulose 

 particles. In the mature conidiophore these fibrils were in spiral arrange- 

 ment in the secondary lamellae. The primary wall in this strain of Asper- 

 gillus was found to be comparatively thin, non-doubly refractive, and 

 largely pectic in composition, as indicated (Fig. 100) by its staining with 

 ruthenium red. By similar reactions to ruthenium red the individual 

 fibrils and even the individual cellulose particles were found to be coated 

 with a non-cellulosic substance, one component of which is pectic. The 

 deep yellow coloration of this colloidal coating with iodine solution ex- 

 plained, at the time, Strasburger's earlier observations of protein "micro- 

 somes" which behave similarly in building up the cell wall lamellae. The 

 cellulose ''microsome" is coated with a non-crystalline film containing both 

 protein and pectic material. However, the developmental importance of 

 this characteristic protein reaction was not recognized until later when, in 

 the course of studies of cellulose formation, it was found to come into exist- 

 ence in a protoplasmic matrix rich in protein. 



With these observations of bacteria and fungi as a basis, a comparison of 

 young cotton fibers in various stages of development showed the presence 

 of similar cellulose particles and similar stages of fibril formation. In the 

 cotton fiber, however, the quantity of colloidal material is greater than in 

 the conidiophore of A . niger and had previously obscured the brightness of 

 the cellulose particles in polarized light. The larger amounts of colloidal 

 material were associated in the cotton fiber with strength and flexibility; 

 the smaller amounts in the conidiophore with weakness and brittleness. 



These results were published by Farr and Eckerson under the title "For- 

 mation of cellulose membranes by microscopic particles of uniform size in 

 linear arrangement." ^o The broader botanical attack upon cell-membrane 



Figure 100. a, Single bacteria from cultures of Acelobader xylinus in positions of 

 extinction and brightness in polarized light with selenite screen (2700 X). b, Mount 

 shown in a without selenite screen (2700 X). c, Sulphuric acid-iodine reaction in 

 A. xylinus (1950 X). d, Pectic coating upon the surface of A. xylinus stained with 

 ruthenium red (1950 X). e. Cellulose particles separate and in chains in young spor- 

 angiophore of Aspergillus niger. Polarized hght (700 X). /, Portion of young spor- 

 angiophore of A. niger showing original pectic membrane and pectic coating upon the 

 individual cellulose particles stained with ruthenium red (1150 X). g, Cellulose particles 

 in the process of fibril formation in sporangiophore of A. niger (1900 X). h, Tip and 

 base of young sporangiophore of A. niger showing earhest cellulose membrane formation 

 near base of stalk. Polarized light (1700 X). k, Developing sporangiophore of A. niger 

 showing increasing thickness of cellulose membrane in lower portion. Polarized light 

 (1700 X). m, Portion of stalk of mature sporangiophore of A. niger showing crossed 

 spiral arrangement and reversal area of cellulose fibrils. Polarized light (1150 X). 

 n, Another portion of a mature sporangiophore of A. niger showing more frequent areas 

 of reversal. Polarized Hght (1150 X). o, Mature sporangiophore of A. niger showing 

 thick cellulose membrane throughout its entire length. Polarized light (500 X). p, Por- 

 tion of fiber of Hibiscus spathecus stained with ruthenium red to indicate its outer pectic 

 layer (700 X). r, Portion of intact fiber of H. spathecus showing longitudinal areas of 

 coloration in polarized light (200 X). s, Base of H. spathecus fiber shghtly crushed to 

 bring out crossed spiral arrangement of fibrils (550 X). 



