A Botanical and Economic Study. 83 



large vessels a spiral tracheid is occasionally found. Cells 

 with reticulated markings occupy the area between the larger 

 dotted vessels. The phloem appears as a bright area with 

 sieve tubes and companion cells, while the quantity of bast 

 increases or diminishes in different areas, but is found in 

 largest development in the interior of the stem. 



Leaf.— The leaf is divided into sheath and blade, which are 

 separated anatomically as well as morphologically from each 

 other by the ligule. A partial section across the base of the 

 sheath is shown in Fig. 3, Plate XVI. Examining the upper 

 inner surface first, we find the stereome immediately below 

 the epidermis. The stereome breaks up into discontinuous 

 patches near the overlapped margins of the sheath. The 

 outer lower surface is essentially different. The superficial 

 bundles are covered by an epidermis, the cells of which are 

 strongly thickened on the outer wall for protection against 

 extremes of heat or cold. Stiff, thick-walled, unicellular 

 hairs, associated with the long, narrow guard cells of the 

 stomata, no doubt serve the same purpose. The larger, 

 deeper-lying bundles are normal. The smaller, superficial 

 ones have a less number of cells, noticeably bast cells. The 

 smaller bundles are at places near the margin surrounded by 

 a circle of active parenchyma cells, which contain chlorophyll, 

 and called by De Bary and Sachs the starch sheath, or starch 

 ring. 1 



The upper inner midrib area of the blade at the base shows 

 five or six layers of sclerotic cells (stereome or water tissue) 

 continuous for some distance on each side of the middle line ; 

 near the margin, however, the strengthening layers are dis- 

 tributed in discontinuous patches with reference to large cells 

 between the so-called bulliform cells. Near the tip of the leaf, 

 the fibro-vascular bundles alone strengthen the leaf ; the stere- 

 ome disappears. The swelling of the bulliform cells (Fig. 4, 

 Plate XVI, B) by imbibition of water causes the blade to open 

 out in those leaves which are folded in the bud. They are 

 found only on the upper side of the blade on each side of the 



1 De Bary, Comparative Anatomy ,416; Sachs, Botan. Zeitg., 1S59, 177, Taf. vm, ix : 

 Pringsheim's Jahrb , in, 194. 



