ii6 



LEAF-MOVEMENTS 



the leaf assumes the day -position. In the case of the Sensitive 

 Plant (Mimosa pudica, Fig. 56, B) a similar but very sudden 

 fall in turgiditv results when the leaf is touched or injured. 



The leaves so far considered exhibit a marked difference of 

 structure and appearance between the upper and lower surfaces 

 (dorsiventral type), but this is not always the case. In the Iris 



Fig. 56. — A, Pulvinus of J<unner Bean [Phascolus) and diagrams of trans- 

 verse sections of tlic pulvinus {F'lt.) and the petiole {Pe.). B, Pulvinus 

 of Sensitive Plant IMiniusci pudica). p., pulvinus ; s., stipules. 



and other Monocotvledons, where the leaf -blades stand vertically, 

 the structure is identical on the two sides (isobilateral type). In 

 still other cases, particularly in succulents among British plants 

 (e.g. Wliite Stonecrop, Scdum album), the leaves arc more or less 

 cylindrical, and, apart from the dor5i\"entral arrangement of the 

 vascular l)undles, exhibit radial organisation (Fig. 86, p. 165), 

 with a palisade la\X'r extending uniformly round the periphery. 



