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 joenetrate 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 Panicutn plicatum, when dry, close in a zigzag 

 manner like a fan. 



The bulliform cells of the leaves of Phleuni pratens<i (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 SjJOroholus and others, the bulliform 

 cells are large, the groups numerous, and j)enetrate deeply. 

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

 the time, unless the weather is verv moist. 



Fig. 37.— Transverse section of a small 

 portion of a blade of Sporobolui^ cryp- 

 tandrus showing bulliform cells, in 

 which there is a single large one, 

 deeply penetrating and some smaller 

 .cells at the side. 1 x 175. — (Sudworth.) 



Fig. 38.— Section of a leaf -blade 

 of Hieroch hm alpina. 1 x 34. 

 (Sudworth.) 



Fig. 39.— Section of a leaf-blade of Stipa spartca, well adapted for closing in dry 

 weather. 1 x 3i. — (Sudworth.; 



