238 IOWA ACADEMY OF SCIENCES. 



In cross section (upper figure, Plate XI), the epidermal cells 

 of the two sides appear much alike in shape and size, the lower 

 having a much thicker cuticle, and no hairs or b Jliform cells. 



The upper or inner surface presents the bulliform cells in 

 various forms according to the variety of corn, varying from 

 the wedge shaped, sunken cells to those somewhat exserted 

 and rectangular. Along each side of the bulliform area is often 

 a row of short, spur-like hairs. The function of the bulliform 

 cells is to fold or roll up the leaf. When there is much evap 

 oration the water from these cells is readily given off, and the 

 leaf rolls up, exposing only the outer or lower epidermis, which 

 is thick and smooth, and thus reduces transpiration very mater- 

 ially. 



Beneath the bulliform cells is a line of colorless parenchyma. 

 The veinlets or nerves have well developed fibrovascular bundles 

 with areas of stereome or sclerenchyma, both above and below, 

 which connect with the epidermis, and a line of thick-walled 

 chlorophyll parenchyma on each side. The small mestome 

 bundles are numerous, and about every sixth has more or less 

 stereome between it and the epidermis, mostly on the lower or 

 outer side. The other mestome bundles vary somewhat in size 

 according to their proximity to bulliform cells. They are 

 completely surrounded by the thick walled chlorophyll paren- 

 chyma sheath, and the mesophyll sheath also, but those con- 

 nected with the epidermis are only partly surrounded. 



EXPLANATION OF PLATES. 



Plate IX. Cross section of corn leaf sheath showing fibrovascular bundle, the most 

 common, type ep, outer or lower epidermis; st, stereome; prp, protophloem; p, 

 phloem, c. p. «., chlorophyll parenchyma sheath; d, pitted ducts; a, annular ducts; 

 i.s., intercellular space; 8.8., sclerotic sheath; par.,colorle8S parenchyma; i ep , 

 inner epidermis. 



Plate X. Cross section of keel showing large fibrovascular bundle with a mestome 

 bundle to the right, (See Fig. 13 for small bundle ) Ep, lower epidermis; prp, proto- 

 phloem; d, pitted ducts; a, annular duct; i. s., intercellular space; 8. 8., sclerotic 

 sheath; x, xylem. 



Plate XI. Upper fig. Cross se2tioa of the leaf blade of corn. Bp, upper epidermis. 

 b, bulliform area surrounding the base of a hair; c. p., colorless parenchyma; 8. 8., 

 sclerotic sheath (chlorophyll bearing) of the mestome bundles; par, parenchyma 

 Lower fig. Upper surface section of epidermis; b, bulliform area; ep, epidermal 

 cells; 8fo, stomata. 



