very conspicuous feature in a transverse section (figure 

 26) are soft and yielding during the growing period. 

 The bundles in question accompany the fibro-vascular 

 bundles, and the component cells are fiber-like, with 

 highly elastic walls, seen as darker groups of cells in 

 figure 26. 



Chemical Characters of the Tissues. 



When the cell-walls are first formed, they are com- 

 posed of cellulose, with a layer (the primary mem- 

 brane) of pectose between the adjacent walls. As de- 

 velopment proceeds, additional substances (lignin- 

 bodies) the chief of which passes under the term lignin 

 are added to the walls. 



Stem. — In the mature straw, all the cell-walls become 

 strongly lignified with the exception only of the 

 phloem, the thin-walled xylem (wood) lying on either 

 side of the primary wood, the collapsed pith cells, and 

 the chlorenchyma. The lignified tissues therefore are 

 the epidermis, 7 all the fibers, all the wood vessels, 

 (tracheids) and the parenchyma (save the inner pith 

 cells and chlorenchyma) (figure 4). On account of the 

 completeness of lignification the cellulose of straws 

 (grain straws) is regarded chemically as lignocellulose. 



Figure 26. — Sector of a transverse section of a false node 

 (leaf base) of wheat. xl05. 



Leaf Sheath. — In the basal region the fibers between 

 the bundles and the lower epidermis are wholly ligni- 

 fied. Of the long cells (1,1, figure 25) some, ut not all, 

 are lignified, those namely which lie near the middle 

 vertical plane of the bundle. The true fibers occur, 

 as they do next the upper epidermis in the left hand 

 (the' larger) bundle in figures 25, these are lignified. 

 The lower (outer) epidermis is weakly lignified only, 

 the inner not at all. The fiber and xylem (except the 

 soft xylem) are also lignified. The parenchyma is not. 



In the upper part of the leaf sheath only the fibers 

 between the bundles and the outer epidermis are ligni- 

 fied, as also the fibers and xylem vessels of the bundles. 



7 The lignin reaction proceeds very slowly in the out- 

 ermost fibers and in the epidermal cells. This seems 

 to be due to other substances possibly of the same na- 

 ture as that which renders the cuticle waxy. A light 

 yellow color is noticeable in these tissues. 



The thin papery leaf margin is unlignified for some 

 distance from the edge, probably as a result of early 

 desiccation. 



In the false node there is no lignification at all, ex- 

 cepting only the xylem (wood) vessels. 



The epidermis is clothed by a very delicate mem- 

 brane which extends over the whole surface of the 

 plant, the cuticle. This membrane is impregnated with 

 a wax-like substance which renders it very hard and 

 resistant, and gives it a highly glossy finish character- 

 istic of straw. It repels even hot water after consider- 

 able boiling. There is some evidence also that the in- 

 ner cells of the parenchyma and the associated cells 

 are more or less impregnated with wax-like materials, 

 since their primary walls are very resistant to concen- 

 trated sulphuric acid even after twenty-four hours 

 treatment. This may be due simply to a high degree 

 of lignification however. 



There is furthermore a considerable degree of silici- 

 fication of both cuticle and more of less of the tissue 

 beneath. The presence of silica gives to the straw a 

 corresponding degree of hardness and smooth finish. 

 The amount of silica is sufficient in many cases to pre- 

 serve the form of the cells even after the complete ex- 

 traction of the cellulose and other»matprials by suitable 

 reagents. An analysis of four samples of straw for 

 silica gave the following percentages of the total dry 

 matter. 



Barley 2.07 



1.78 



Oats 3.46 



3.46 



Rye 2.18 



2.14 



Wheat 2.30 



2.44 



It is the amount of silica in the superficial tissues 

 which renders the surface so very hard and resistant. 

 It is well known that the same result is seen in the sur- 

 face tissues especially of bamboo, rattan, and the like. 8 



Zacaton (Blicampes macroura) according to Brand 

 and Murrill (1915) contains silica to the amount of 6.5 

 to 7.5 on the total straw. This is "very high." 



In the preparation of paper pulp the pectose is al- 

 tered, setting the cells free from each other, and the 

 cells are more or less delignified. The deli<?nification 

 is carried on much further in bleached pulp than in 

 the unbleached pulps. Papers subjected in manufac- 

 ture to a 20 per cent and to a 15 per cent lime cook, and 

 a. "Kraft" paper all showed pronounced lignin reac- 

 tions with the Klason and with the Cross and Bevan 

 methods, while bleached papers from wheat straw sub- 

 jected to a 6 and a 10 hour soda cook, and from oat. srave 

 only verv slight lignin reactions. An unbleached" oat 

 gave a distinctly stronger lignin reaction. 



8 The following figures are afforded by C. Wehmer 

 (1911) : 



Total ash 



of which silica 



constitutes 



• • • 50-60 parts 

 . . . 50-66 " 

 . .. 60-70 " 

 . . 50-60 " 

 higher than the previous 

 sriven. but of course no adeouate comparison may be 

 instituted without due regard to place effect and other 

 possible conditions. 



Barley 5-7 % 



Oat — 



Rve 5-10 



Wheat 3-5 



These figures are much 



