258 MOVEMENT IN PLANTS. 



the leaves pass in the evening from a horizontal to a vertical posi- 

 tion. The cotyledons of some seedlings, e.g. Radish, spread out 

 during the day and close up at night. Observations should be made 

 on all these plants. 



367. The Movements of Pulvinate Leaves are of 



greater interest. In the leaves of various plants (especially 

 Leguminosae and Oxalidaceae) , movements occur which 

 depend not upon growth but simply on unequal osmotic 

 pressure on the opposite sides of the swollen leaf -base 

 (pulvinus). We have seen that tropistic curvature is 

 frequently due in the first instance to increased turgescence 

 of the convex side of the curving organ, this being followed 

 by growth in length of that side. In the movements of 

 pulvini there is no permanent elongation of the convex 

 side, i.e. no growth occurs. 



The movements of the pulvinate leaves of Mimosa have 

 already been studied in detail. 



Examine the leaves of Wood Sorrel, Clover, Phaseolus 

 (French Bean, Scarlet Runner). Note that in Phaseolus a 

 pulvinus is present not only at the base of the petiole, but 

 also at the base of each leaflet. Study the day and night 

 positions of the leaves of these plants, as well as of others 

 showing sleep movements, e.g. False Acacia (Eobinia). 



368. Experiments with Clover. Note that by day 

 the three leaflets are spread out horizontally from the top 

 of the stalk ; at night the two basal leaflets rotate until 

 they stand in the vertical plane, then they swing round 

 till their upper surfaces come together, and finally the end 

 leaflet rotates upwards through 180 and comes down like 

 a roof over the edges of the other two leaflets. 



(a) On a bright day, cover with a flower-pot or dark-box 

 a Clover plant growing in the open, or one dug up and set 

 in moist soil in a saucer ; note that in about half an hour 

 the leaves have assumed a night position. 



(&) Keep a Clover plant in darkness for a week, and 

 note that the leaves ultimately assume a position re- 

 sembling the day position, except that the leaflets are more 

 drooping. 



