MEASURES FOR I'ROTECTIXO GROWING ri.ANTS KKoM LOSS OF HEAT. 



533 



as the turgidity of the cells increases iu one of the iialves of tlie pulximis, in con- 

 sequence of an increased afflux of water, this half elongates, hulges out, becomes 

 convex, and exerts a stronger pressure than tlie opposite half, so that the latter 

 becomes concave and nuich contracted. The supple portion of the bundle-strand 

 between the two halves of the cushion becomes bent, and the leaflet, whose stiff 



133.— Alteration of Position of Lciflcts iu Conipouud Leaves. 



I Leaf of Mimosa LUidheimerij seen from above, iu day position. 2 The same iu ui^lit position. ' Lc.if of Amorpha fruticosa 

 in day position. * The same in !iigtlt position. * Leaf of Coronilla varia in day position, o Tile same in night iiositiou. 

 ' Leaf of Tetragonolobus siliquosui in day position, a The same in night position. 



midrib is formed by the continuation of the bent bundle-strand, is inclined over 

 in the direction of the concave half of tlie pulvinus. If the increase of turgidity 

 occurs alternately first in the one and thou in the other half of the pulvinus, the 

 leaflet will also be bent now to the one, then to the other side; and if the leaf- 

 support has a horizontal position, an alternate rising and sinking of the leaflet will 

 occur. It is to be noticed here that the leaflet itself remains actually quite passive, 

 and that the pressures which have come into play only operate in tlie pulvinus. 

 The commonest stinmlation to periodic alteration of the turgidity in the piilviiii 



