264 GROWTH OF PLANTS 



chemical properties of a bacterial membrane and one less likely to affect 

 its natural properties than many of the staining techniques in current use. 

 They necessitated some changes in microscopic technique, however, the 

 most important of which consisted in the readjustments of the illuminating 

 system. This involved mainly the lowering of the intensity of the artificial 

 light by suitable rheostat control, so that the structural differentiations in 

 the diminutive organisms would not be obscured by a flood of bright light. 



The results of these bacterial studies were of interest in the light of 

 current attempts to "synthesize" cellulose membranes by growing A. xyli- 

 nus in glucose solutions.^^ In these contemporary Canadian experiments 

 the process of cellulose formation was considered to be intercellular, the 

 cellulose molecules having been synthesized directly from the sugar mole- 

 cules in the nutrient medium and deposited in long, well-oriented chains of 

 cellulose unit-cells. At the request of and from cultures furnished by 

 Dr. H. L. Hibbert, the entire "membrane" was found by Farr and Ecker- 

 son 2" to consist of bacterial organisms with no true intercellular substance. 

 The single bacterium is composed of a protoplast surrounded by a cellulose 

 membrane which, in turn, is covered with a layer of gelatinous material 

 which reacts positively with the ruthenium red test for pectic substance 

 and negatively to the H2SO4 and I2KI test for cellulose. Studies in both 

 ordinary and polarized light at low and high magnifications produced no 

 evidence of continuous, long chains of cellulose in the membranes. They 

 did indicate, however, extreme regularity in directional arrangement of the 

 strands of the aerobic organisms as they grew in thin layers upon the sur- 

 face of the nutrient media. 



The development of microscopic techniques by means of which such 

 bacterial membranes could be analyzed was of even greater importance. 

 The optical systems, thus illuminated, were then available for use in exam- 

 ining other types of plant cells. One of the first of these which was studied 

 was the developing conidiophore of Aspergillus niger. Dr. Charles Thom 

 had called to Mrs. Farr's attention structures in the wall of the mature 

 stalk of a certain strain of this fungus which closely resembled the spiral 

 fibrils in the wall of the cotton fiber. In the protoplasm of the very young 

 stalks tiny granules were found which gave the characteristic cellulose 

 reaction with sulphuric acid and iodine. As the stalks developed they were 

 carefully mounted for observation in both ordinary and polarized light. It 

 was thus found that, within the limits of one sporangiophore, the successive 



Figure 99. Hand-colored photomicrographs of portions of fibers in plane-polarized 

 light: a to r from Upland cotton, s and t from Jungle cotton; long axes of portions oriented 

 at 45° with reference to the plane of vibration of the light; d, n, o, and r slightly swollen 

 in a solution of ammonium thiocyanate; a, b, c, I, m, s, and t photographed with the 

 analyzer; d, n, 0, and r without the analyzer; c and m colored with the selenite plate 

 (red of the first order) ; a, b, d, I, n, o, r, s, and t without the selenite plate; a, b, c, I, and 

 m, 690 X ; d and n, 810 X',o,r, s, and t, 1200 X . (Coloring of photomicrographs was done 

 by Miss Flora White.) 



