MOVEMENTS OF LEAVES. 



In vernation (while the leaf is very 

 young in the bud) the leaves take the 

 same positions as when full grown and 

 dried, though the bulliform cells at that 

 time, are very small, as we should ex- 

 pect. The very young leaves of Dactylis 

 glomerata (orchard grass) and Poapraten- 

 sis (June grass) are conduplicate, while 

 those of Phleum pratense vlimothy), are 

 convolute. Some young leaves combine 



these two modes more or less, and may 



FIG. 30. A cross section of 

 be conduplicate in the middle and con- young leaf of Aira caespitosa, 



showing its mode of vernation 



volute on the margins. within the sheath. 1x33. 



The Movements of the leaves of some Leguminosae are very 

 quick, in most grasses they are quite slow, depending on the light 

 and change of moisture. In the blades of grass the motion when 

 drying, consists in the approach of the sides when conduplicate, 

 or in rolling or unrolling when convolute . and in tortion when 

 turning the lower surface to the sun. 



In 1858, Mr. Duvol-Jouve was surprised to see the leaves of 

 Leersia oryzoides (rice cut-grass), move quite quickly, as he 

 brushed them. The motion begins at the apex and extends down 

 to the base, and is convolute when closed. Other species of this 

 genus behave in like manner, as also does Sesleria coerulea. 



A drop of water on the section of the leaf of the latter causes 

 it to expand instantly. The same is true of a leaf of Poa 

 pratensis or of Dactylis. Some leaves open very slowly and then 

 only when quite moist, as in case of Lygeum sparteum, or Nardus 

 stricta. 



The annual species of ^'raand Chamagrostis minima are abso- 

 lutely destitute of motion. 



Many remain rolled up when dry, and unroll at night when 



