142 Mr. Worsley-Beuison on the 



only at the upper part. If a struma at the tip of a leaflet was 

 touched, the foldiug of the leaflets went from tip to stalii-joint, 

 the closing of one pair being sufl&cient to communicate the dis- 

 position to close to the neighbouring pair. If the lowermost 

 pair was made to close, the impulse travelled from joint to ti^J 

 by the same sympathetic influence. After depression had 

 ensued, a fresh flow of water into the emptied cells raised the 

 leaf, and the lealiets opened again. This " water-theory " was 

 affected by Gardiner's researches on ' Continuity of Protoplasm.' 

 He found this continuity in the jjuliinus, a discovery which 

 would probably lead to the conclusion tiiat the movements had 

 close relation to the continuity of protoplasm. All this was 

 effected periodically in Mhnosd by the light and heat of the 

 atmosphere, which were the stimuli ; sleep commenced just 

 before sunset, waking preceded the sunrise. Thus Minivsa 

 closed its leaflets and drooped its leaves gradually during the 

 day, and during the night gradually raised the leaves and opened 

 the leaflets, which was the reverse to the general habit of sensi- 

 tive plants. 



The Mimosa had a tendency, on a succession of mechanical 

 shakings, of getting used to it. Desfontaines proved this by 

 carrying a Mimosa on a stage-coach journey, when, although at 

 fij'st affected by the jolting, after a time the plant kept its leaves 

 extended. Another instance of this movement was afforded by 

 the telegraph-plant, iJcsmodium yijrans, so-called from its motion 

 resembling that of the two arms of the old-fashioned Semaphore 

 signal. The leaf was trifoliate, the terminal leaflet being very 

 large, the lateral leaflets very small. During the day the end 

 leaflet gradually followed the sun, sinking slowly until its under 

 surface lay quite back against its own stalk or petiole. The pair 

 of side leaflets, on the other hand, moved up and down with a 

 jerky motion, from about 8.30 a.m. until between 3 and 4 a.m. 

 of the next day. Both the end and lateral leaflets moved in 

 virtue of pidvini at the base of their petioles. The end one 

 seemed to be influenced by the sun, but the lateral leaflets weie 

 apparently independent of external influences. Their move- 

 ments were spasmodic, stopping occasionally as if to overcome 

 some unseen obstacle, and seemed to result from the alternate 

 lengthening and shortening of one side of the petiole. Their 

 motion was on their own axis, beiug circular as well as up and 

 down, and each moved alternately with the other, the down 

 stroke being rapid, the up stroke more steady. As the terminal 

 leaflet fell, its petiole rose, so that at night the leaves were all 

 drooping, and the petioles upright, thus greatly reducing the 

 diameter of the plant. There could be no doubt that the object 

 of the sleep of leaves was, that they might expose less of their our- 

 faces to the effect of chill by radiation from those surfaces at night. 



