THE OCCURRENCE OF CALLOSE IN ROOT HAIRS. 



CHARLES S. RIDGWAY 



Alabama Polytechnic Institute, Auburn, Alabama 



In the pertinent literature at hand but one reference has been 

 found concerning the occurrence of secondary thickening in root- 

 hairs. Kiister^ states that strong cellulose thickenings have been 

 found in root-hairs of plants which have been subjected to dis- 

 turbances of nutrition and the influence of growth-checking 

 factors. The presence of thickenings on the walls of such struc- 

 tures as rhizoids, pollen-tubes, and various algae and in the hy- 

 phae of fungi is well known, and the thickening substance in 

 many of these cases has been found to consist of callose,^ but 

 apparently no mention has been made of the occurrence of this 

 substance in root-hairs. Recently, however, the writer noticed 

 that some of the root-hairs of young plants of Panicum sp. were 

 very strongly refractive under low magnification and presented 

 an entirely different appearance from that of the majority, which 

 were of the usual type. Closer examination showed that the differ- 

 ence in appearance was due to a marked thickening of the wall of 

 the hair and of the outer tangential and the radial walls of its 

 enlarged basal part. A large number of the roots of the grass 

 were then examined in water, and the thickened hairs were found 

 to be of frequent occurrence. 



In preparations mounted in glycerine and examined after 24 

 hours it was found that the clearing effect of the glycerine had 

 heightened the contrast between the thickened and normal hairs, 

 as regards their power of refraction. In these preparations the 

 outer cellulose part of the wall and the layered structure of the 



* Kuster, E., Pathologische Pflanzenanatomie. Jena 1903, p. 63. 



- Kuster, E., loc. cit., Mangin, L., Sur la callose, nouvelle substance fundamen- 

 tale existant dans la membrane. Compt. Rend. 110 : 644. 1890 Zimmerman, 

 A. Botanical Microtechnique, pp. 163-166. 1893. 



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