40 GRASSES OF IOWA. 



Bulliform cells. — Between the nerves occur peculiar epidermal 

 cells which are wedge-shaped; these are known as bulliforoa 

 cells Hackel* says these are arranged in the form of a fan 

 whose growth and expansion causes the blades to open out; in 

 those leaves which are rolled in the bud these cells are only 

 found on each side of the mid rib. Excellent bulliform cells 

 occur in orchard grass, Spartina, etc. In some species of 

 Sporobolus, the leaves are rolled up much of the time. Where 

 the leaves open the bulliform cells are large and penetrate 

 deeply. la Festuca tenella and some other species of the genus 

 the leaves do not open and Lence bulliform cells are absent, or, 

 but slightly developed. This is also true of Stipa and Nardus. 

 It is owing to this peculiar cell development that the leaves of 

 Sporobolus roll up so easily when they become dry. It requires 

 excessive moisture to open them. Excessive transpiration dur- 

 ing dry weather causes the leaf blades to roll up because they 

 have lost their turgescence, but when the atmosphere is moist 

 they flatten out. The bulliform cells afford protection to our 

 wild prairie grasses, and thus they pass the hot, dry winds 

 unharmed while many cultivated grasses are injured. The 

 lower side of the leaf is protected by the strongly developed 

 cuticle which prevents transpiration. 



Professor Beal, who has made a study of the bulliform cells of 

 many leaves, says as follows: "The leaves of Poa have two 

 bands, one on each side of the middle. Andropogon squarrosios 

 has one band on each> side of the middle and a small one at 

 each edge. The leaf of the Phleum pratense has one band of 

 several shallow cells on each side of the middle and others 

 between the veins. The leaves of Zea mays have a band 

 between each two primary bundles and above each third class 

 buridle. The leaves of the Leersia oryzoides have numerous 

 bands on the upper surface on each side of the middle, and 

 on each side of the keel on the lower side. The leaf Amphicar- 

 puyn pui'shii has opposite bands of bulliform cells on both sur- 

 faces. Those above are most prominent. In case of the 

 leaves of Panicum plicatum the bands of bulliform cells are first 

 on the upper side then on the lower, and are found in grooves. 

 The leaves of ^Jidropo^onprinoides have large epidermal cells of 

 nearly uniform size, distributed along the surface, excepting 

 over the veins. " 



*True grasses, EagUsh translation, Lamson, Scrlbner, and Soutbworth. 9. 



