24 



MOVEMENTS OF LEAVES. 



the dew is on, while others rarely ever open at all, but remain 

 closed. 



The leaves of Leersia (rice cut-grass) are -most instructive with 

 their bullif orm cells above and below. These penetrate the blade 

 deeply and make it very sensitive. In a warm day a brisk rub, 

 or more than one between thumb and finger, causes it to close in a 

 few seconds. After a short interval the leaf opens again, when it 

 will be ready to respond to the same experiment. 



The leaves of Panicum plicatum, when dry, close in a zigzag 

 manner like a fan. 



The bullif orm cells of the leaves of Phleum pratense (Timothy) 

 and Alopecurus pratensis (meadow foxtail) are not very large, 

 and do not penetrate deeply. Such leaves are not good " rollers. " 



In case of leaves like Sporobolus and others, the bulliform 

 cells are large, the groups numerous, and penetrate deeply. 

 These leaves are likely to remain rolled up for a good portion of 

 the time, unless the weather is very moist. 



FKJ. 37. Transverse section of a small 

 portion of a blade of Sporobolus cryp- 

 tandrus showing bulliform cells, in 

 which there is a single large one, 

 deeply penetrating and some smaller 

 Cecils at the side. 1 * 175. (Sudworth.) 



FIG. 38.-Section of a leaf -blade 

 of Hierochloa alpina. 1x24. 

 (Sudworth.) 



FIG. 39. Section of a leaf-blade of Stipa spartca, well adapted for closing ii 

 weather. 1 x 34. -(Sudworth.) 



