20 THE JOUKNAL OF INDIAN BOTANY. 



tangential and also by radial lines, which latter appear to be continua- 

 tions of the middle lamellas between the cells, (fig. 3.) The tangential 

 lines are clearly due to stratification of the substance produced by 

 successive changes in its composition affecting its refractive index, for 

 they are progressively further apart and fainter, and the presence of 

 the radial lines clearly indicating the lateral limits of each cell, shows 

 that the secretion or modification of each cell takes place indepen- 

 dently of those of contiguous cells. 



The secretion does not take up any of the ordinary protoplasmic 

 stains, such as eosin, osmic acid, or hsematoxylon ; nor could we 

 obtain any reaction with methyline-blue, Schultz solution or iodine. 



We conclude that the secretion is due to a modification of the 

 cell-wall, and though controlled and brought about by each cell 

 independently, is not a direct product of its protoplasm. But that it 

 is not a gum or mucilage in the ordinary sense is shown by the fact 

 that it does not swell and dissolve in water at the ordinary tempera- 

 ture, nor take up any cellular stains nor show any cellulose reaction . 



The Boot-hairs. 



As stated above, the root-hairs are found only on parts of the root 

 near the surface of the sand. A few inches down they are cut off by 

 the exodermis, which is formed as usual in monocotyledons, and 

 shrivel up. But near the surface there is no exodermis, and the 

 root-hairs formed while that part was still young persist apparently 

 indefinitely. 



The Beg ions of the root. 



There are three regions in the root : — 



I. From the tip to the region of the exodermis the surface is 

 covered by the secretion. This may be two to six inches long and the 

 surface is white, smooth and glistening. 



II. In the region of the exodermis the surface tissue is dead and 

 brown. It is in this region that the short rootlets are found. 



III. From the exodermal region to the surface, for a length of two 

 or three inches as a rule, the piliferous layer remains fresh, the root- 

 hairs persist and adhere firmly to grains of sand. 



The existence of a secretion by the piliferous layer has been 

 noted, we believe, in only a few grasses, which grow in the Algerian 

 Sahara. The chief of these is Aristida pungens. E. Price (2) who 

 has examined the secretion, pointed out that in Aristida it binds 

 together the sand particles with a tubular sheath into which root- 

 hairs run and are thus enabled, probably, to take up moisture from a 

 larger volume of sand. 



