188 MIMOSA. [CH. VIII 



fall within an hour to 11° or 12° C.\ when the plant will 

 be found to have lost all irritability. By adding hot 

 water the temperature may be raised to about 20° 0. in a 

 quarter of an hour, when the irritability will have 

 returned. 



(235) Mimosa : effect of darkness. 



If Mimosa is kept in the dark for several days it loses 

 its sensitiveness. The plant should be kept in a damp 

 atmosphere in a greenhouse at a temperature of at least 

 16° — 17° C. The best plan is to place the flower-pot in 

 a tray of wet sawdust and to invert over it a tin cylinder, 

 the rim of which should sink into the sawdust. We find 

 that 4 or 5 days are needed to destroy sensitiveness. In 

 one of Sachs' experiments" a plant was placed in the dark 

 at 9 p.m. Sept. 24 and on Sept. 27 at 9 a.m. sensitiveness 

 had almost, and on 28th, quite disappeared. It was 

 then exposed to light and took some days to recover. 



(236) Mimosa: continued stimulation. 



A light stick about 25 cm. in length is transfixed by a 

 needle at about 6 cm. from one end ; the ends of the 

 needle are pushed into rubber corks, which are held in a 

 clamp. Since the needle cannot turn easily in the 

 rubber which supports its two ends, the stick will stand 

 out horizontally: a slight blow on the short end of the 

 lever makes the other end jump up, and the elasticity of 

 the corks brings it back to its old position; if repeated 



1 The lower limit of temperature is higher than this, namely, about 



2 Physiologic Vigetale. French Trans., p. 49. 



