170 THE I' I, ANT LIFE OF MARYLAND 



region of the blade, magnified 12 times. It may be observed that 

 the leaf is partly rolled up, with the upper surface inward. A 

 small piece of the leaf is more highly magnified in Fig. 2 (x40), 

 and it may now be seen that the upper surface of the leaf is deeply 

 grooved by a series of depressions running lengthwise on the upper 

 face. Vascular bundles of two ranks are present, situated in the 

 areas marked out by the grooves. The internal structure can, how- 

 ever, be better made out in Fig. 3 (xSO). Each birndle is encircled 

 by a row of large cells which in the fresh state are seen to be either 

 colorless or else scantily supplied with chloroplastids on the side 

 away from the vascular bundle. These cells appear to function 

 largely as water reservoirs. To the right and left of these storage 

 cells are small cells richly provided with chloroplastids and sep- 

 arated by intercellular spaces — the spongy tissue of the leaf. This 

 layer is well shown in Fig. 5. A band of mechanical tissue may 

 be seen at each end of the group of storage cells, immediately be- 

 neath the upper and lower epidermis of the leaf. Thus in each 

 of the units into which the leaf is divided there is a division of 

 labor among the conducting, storage, assimilatory and mechanical 

 tissues. At the foot of the grooves may be seen in several of the 

 figures a group of rather large cells whose outline is irregular owing 

 to collapse of the walls. These are the "bulliform cells," first de- 

 scribed by Duval- Jouve,* and figured for many grasses, e. g., by 

 Holm ; f to their shrinkage and collapse is due the rolling up of 

 the leaf when the water supply is scanty compared with transpira- 

 tion. Beneath each group of "bulliform cells" there may be seen 

 in a fresh specimen a large cavity bounded laterally by the green 

 cells ; in the preserved material these cavities almost entirely col- 

 lapse, but indications of them are visible in several of the figures. 

 The "bulliform cells" are rather small in the species under consid- 

 eration, but their action is doubtless supplemented by the collapse 

 of the cavities just described. The grooves next claim our atten- 

 tion. It will be noticed that their depth is a little less than half 

 the thickness of the leaf, and in the curled leaf they are exceed- 



*Ann. Sci. Nat. Bot, vol. vi, pt. 1, 1875, pp. 294-371. 



tHolm, T. A study of some anatomical characters of North American 

 Gramineae. Botan. Gaz., vol. xvi, 1891, p. 166. 



