Chap. VII 



SLEEP OF LEAVES. 



373 



perpeniicularly down, the movement of its apex was traced 

 until 10.30 P.M. ; and during this whole time it swayed from 

 side to side, completing more than one ellipse. 



Bauhinia (Tribe 15).— Fig. 156 



The nyctitropic moyements 

 of four species were alike, 

 and were highly peculiar. 

 A plant raised from seed 

 sent us from South Brazil 

 by Fritz Miiller, was more 

 especially observed. The 

 loaves are large and deeply 

 notched at their ends. At 

 night the two halves rise 

 up and close completely 

 together, like the opposite 

 leaflets of many Legumi- 

 nosse. With very young 

 plants the petioles rise con- 

 siderably at the same time ; 

 one, which was inclined at 

 noon 45° above the hori- 

 zon, at night stood at 75° ; 

 it thus rose 30°; another 

 rose 34°. "Whilst the two 

 halves of the leaf are closing, 

 the midrib at first sinks 

 vertically downwards and 

 afterwards bends back- 

 wards, so as to pass close 

 along one side of its own 

 upwardly inclined petiole; 

 the midrib being thus di- 

 rected towards the stem or 

 axis of the plant. The angle 

 which the midrib formed 

 with the horizon was mea- 

 sured in one case at dif- 

 ferent hours: at noon it stood horizontally; late in the even- 

 ing it depended vertically ; then rose to the opposite side, and 

 at 10.15 P.M. stood at only 27° beneath the horizon, being 

 directed towards the stem. It had thus travelled through 153° 



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