36 GRASSES OF IOWA. 



The primary bundles open on both inferior and superior sur- 

 faces. Leptome is in direct contact with stereome. The had- 

 rome is separated from it by corlorless parenchyma. Mid- 

 nerve consists of only one bundle, and with the exception 

 of size, the large amount of stereome and colorless parenchyma 

 is the same as that of species adapted to open ground , 



The colorless parenchyma occurs beneath all primary 

 bundles, while a sheath encloses all the bundles. Stereome is 

 abundant on both inferior and superior surfaces of the interme- 

 diate bundles. Mesophyll surrounds all the secondary bundles 

 and occurs between the other two types, and on the inferior por- 

 tion of the intermediate type.* In maize, according to Combs, 

 tie sheath in cross section shows, beginning at the upper 

 surface, the epidermis of large, thin-walled cells, immediately 

 inside of which is stereome in patches, which are located oppo- 

 site the large bundles on the outer side. Then comes the 

 inner area of the sheath, made up of large, polygonal, color- 

 less, thin-walled parenchyma cells. 



The outer or lower surface of the sheath presents an entirly 

 different aspect and varies greatly with the variety of corn. 

 Generally speaking, it is more or less ribbed, caused by the 

 large fibro- vascular bundles. The creases have colorless 

 unicellular hairs which are usually not developed on the epi- 

 dermis over the bundles. The epidermal cells are small 

 and thick-walled, and protect the p'ant against drouth and 

 other injuries. Beneath the outer epidermis occur the bundles 

 referred to above, usually with intervening smaller ones, but 

 this varies with different corns. For example, a Mexican 

 corn, number 1, shows two sizes of bundles not connected with 

 each other, forming no external ridges, and the epidermis 

 shows only a few very short spur-like hairs, while a form from 

 South America shows heavy ridges, many hairs, and only one 

 kind of bundle. 



In all cases there exists an area of stereome between the 

 bundles and the outer epidermis. 



The only chlorophyll in the sheath is located in the chloro- 

 phyll parenchyma sheath which surrounds the bundles, 

 except a portion on the outer side which is occupied by 

 stereome. 



The anatomy of the sp:cies thus far considered here, are 



*PfOC. la. Acad. Scl., 5: 201. Coatr. Bot. Dept. la. Sbatj OoUege of Agr. and Mech. 

 Arts. 10: 6. 



