528 LIFE MOVEMENTS IN PLANTS 



an erectile movement of the leaf of Mimosa, diminution 

 of turgor inducing the opposite movement of fall. Kraus 

 and Millardet have shown that a diurnal variation of 

 tension takes place in the shoot of all plants, which is 

 presumably indicative of variation of turgor. This varia- 

 tion of turgor in the shoot must have some effect on the 

 lateral leaves. But the leaves are subjected to conditions 

 which are absent in the stem. The erect stem is, for 

 example, free from geotropic action, whereas the lateral 

 leaf is subject to it. The effect of turgor variation in the 

 shoot on the movement of leaves may be, and often is. 

 overpowered by the predominant geotropic action. I shall, 

 later on, refer to this question in greater detail. 



Autonomous movemetits : Experiment 202. — The lateral 

 organ, say the leaf or leaflet, may have an autonomous 

 movement of its own. In some, the autonomous move- 

 ment may be relatively quick ; the complete pulsation in 



Fit). 1S8. — Arrest of pulsatory movement of leaflet of Desmoditim flj/rans l)y 

 light from above and gradual restoration on cessation of light. Up-movement 

 represented by up-curve. 



Desmodium gyrans may be as short as a minute or so. I 

 find that this autonomous movement becomes modified or 

 even arrested by the paratonic effect of light. This is 

 seen in figure 188, where light applied from above is 

 seen to arrsst the pulsation ; the normal activity is, how- 

 ever, restored on the stoppage of light. 



