ments in the shape of the aforesaid rings and spirals. 

 The large wood cells (vessels) are about 40 microns in 

 diameter (micron = 0.001 millimeter), while the small 

 ones are about 7 to 8 microns, or thereabout, in dia- 

 meter, roughly about one-fifth the diameter of the large 

 vessels. 



Placed radially and on the outside of the wood, form- 

 ing as it were the forehead of the f ase, is a small group 

 of very thin Availed cells with very narrow lumina (ph. 

 figure 24). This is the phloem, concerned chiefly in 

 the movement of food materials. The cells are of two 

 kinds, sieve tubes, which have thickened end walls and 

 more slender cells lying alongside them,' the comparison 

 cells. Like the wood cells, they are elongated elements, 

 very slender and delicate, and usually disappear dur- 

 ing pulping, and contribute not at all -to the final pro- 

 duct. 



Surrounding' the wood and phloem is a narrow layer 

 of fibres (f, figure 24), or rather fiber-like cells, with 

 pitted walls and somewhat oblique (about 45 degrees) 

 or transverse end walls. The fibers on the outside of 

 the phloem (between it and the epidermis) are numer- 

 ous enough to form a small bundle. This is the case 

 also on the inside of the xvlem (toward the center of 

 the stem). The lateral walls when seen longitudinally 

 are irregular when they impinge on the surounding 

 parenchyma. While contributing to the "fibers" of 

 pulp, they constitute only a small proportion of shorter 

 elements. 



Internal Structure of the Leaf Sheath. 



The leaf is composed of elements which are quite 

 similar to those above described for the stem, but ar- 

 ranged somewhat differently, due to the fact that the 

 leaf is a flattened organ, the upper surface (which lies 

 against the stem) being smooth, and the lower ribbed. 

 In a transverse section (figure 25) it is seen to be seg- 

 mented into similar areas of loose parenchyma which 

 behaves quite as does the pith in the stem, breaking 

 down early to leave cavities. Each partition is corn- 



Figure 24. — Transverse section of a single bundle from 

 the stem of wheat, x 232. f., fibers; ph., phloem; s., cavity 

 formed by splitting of the tissues away from the primary 

 wood trachea; x., primary wood vessels (tracheae); x o ., sec- 

 ondary wood vessels. 



posed of a vascular bundle, having bundle of fibers 

 (mechanical tissue) between it and the loAver (outer) 

 epidermis, and a group or bundle of larger, much elon- 

 gated and fiber-like cells between it and the upper 

 (inner) epidermis. The parenchyma which fills the 

 ribs just below the lower (outer) epidermis is com- 

 posed of smaller, chlorophyll bearing cells, through 

 which a small bundle and a group of fibers run, parallel 

 to the larger bundles just noticed. The amount of 

 fibrous material is not inconsiderable, forming approx- 

 imately one-fourth to one-third of the total amount 

 of fiber of an equal length of stem. A peculiar ana- 

 tomical feature of the leaf-sheath is the occurrence of 



/&'• epia 



Figures 20-23. — ectors of transverse sections of the middle 

 region of the lower internode of barley, oat, rye and wheat, 

 resp. x 97. 



Figure 25. — Portion of a transverse section of the leaf 

 sheath of wheat. Note the wide (I, I) thin walled cells just 

 above the bundles, u. epid., upper (inner) epidermis. xl30. 



very long, thin walled tubular cells, (1, figure 25), 

 forming a small group of fibers between the large 

 bundles and the 'upper (inner) epidermis. They can 

 hardly be classed as fibers — or at any rate they cannot 

 be compared with fibers in point of strength, since the 

 walls are thin and the lumen large, measuring 60 mic- 

 rons, more or less. The end Avails are transverse, 

 slightly oblique, or forked. They are relatively few in 

 number, but can usually be found in pulp or straw 

 paper. 



False Nodes. — The above described structure fails 

 almost entirely at the base of the leaf-sheath, where 

 the motile organ or false node occurs. There is an en- 

 tire absence of specialized chlorenchyma, and the par- 

 enchyma is thick walled. The walls, however, in com- 

 mon Avith those of the bundles of fibers, Avhich form a 



