MOVEMENTS OF LEAVES. 



23 



In vernation (wliile tlae leaf is very 

 young in the bud) tlie leaves take the 

 same positions as when full grown ivnd 

 dried, tho^^gh the bnlliform cells at that 

 time, are very small, as we should ex- 

 pect. The very young leaves of Dactyl is 

 glomerata (orchard grass) and Poapraten- 

 sis (June grass) are conduplicate, while 

 those of Pldeum pratense vlimothy), are 

 convolute. Some young leaves combine 

 these two modes more or less, and mQ.y 



. .111 ^^"- <'^'-— '^ cross section of 



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



showinK its mode of vernation 



volute on the margins. witiiin the sheath. ix:ij. 



The Moveiiients of the leaves of some Leguminosaj 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 Avhen 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 oryzuidcs (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 maimer, 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 ^iVaand CUamagrostis winema are abso- 

 lutely destitute of motion. 



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



