84 HarsJiberger. — Maize: 



midrib. According to Duval Jouve, 1 these cells have thin 

 walls and watery interior, and are found on the upper surface 

 between the marginal nerves of the leaf. In grasses which 

 are devoid of such fan-shaped cells, the blade always remains 

 folded up, rush-like, as in Stipa, Festuca, Nardus. In steppe 

 grasses, the blades roll up whenever these cells lose their 

 turgescence by rapid evaporation, and they open again when 

 the water has been restored. The lower side of the leaf has 

 especial protective arrangements against transpiration, in 

 strong cuticle and hypoderm. 2 



The lower surface of the blade shows a larger number of 

 small bundles than the lower surface of the sheath. Either 

 the fibro- vascular bundles enter the blade separately, or a 

 number at first unite to form a strong midrib ; later the single 

 bundles separate one at a time and pass toward the edge of 

 the leaf, giving firmness to the broad lamina. A ring of 

 parenchyma surrounds the small bundles (Fig. 4, Plate XVI). 



The stomata are placed on surface view between two long 

 cells called accessory cells, which were formed when the 

 stomata were differentiated. The process of stoma formation 

 in Indian corn is essentially as follows. A vertical septum is 

 made across one of the long epidermal cells, the small cell 

 cut off being called the stoma mother cell. The two acces- 

 sory cells are now cut off from the mother cell on either side, 

 and the mother-cell divides in two, forming the guard cells- 

 Finally, the lamellae of the wall separating the guard cells split 

 and the opening is formed. 3 According to von Mohl, 4 the 

 stomata on the uninjured leaf of Zea mays widen the slit to 

 TT -g- millimeter. 



Mention must be made of gaps in the epidermis of the leaf. 

 Cracks occur regularly at the apex of the leaf, from which 

 drops of water are expressed. The cracks arise by irregular 

 tearing of the original cowl-like apex of the leaf, when this 

 spreads out flat as it unfolds. 



1 Duval Jouve, Histoire des Feuilles des Graminees, Ann. d. Sc. Nat., vi ser., torn, i, 

 1S75. 294, tab. 4. 



- Hackel, True Grasses. 



3 Campbell, D. H , American Naturalist, xv, 1SS1, 764. 



4 Mohl, H. von, Botan Zeitg., 1856, 697. 



