CHAP. VII. SLEEP OF LEAVES. , 319 



Tropaeolum, Lupinus, Ipomoea, Abutilon, Siegesbeckia, 

 and probably other genera, it is indispensable that 

 the leaves should be well illuminated during the day 

 in order that they may assume at night a vertical 

 position ; and it was probably owing to this cause 

 that seedlings of Chenopodium album and Siegesbeckia 

 orientalis, raised by us during the middle of the winter, 

 though kept at a proper temperature, did not sleep. 

 Lastly, violent agitation by a strong wind, during a 

 few minutes, of the leaves of Maranta arundinacea 

 (which previously had not been disturbed in the hot- 

 house), prevented their sleeping during the two next 

 nights. 



We will now give our observations on sleeping 

 plants, made in the manner described in the Intro- 

 duction. The stem of the plant was always secured 

 (when not stated to the contrary) close to the base of 

 the leaf, the movements of which were being observed, 

 so as to prevent the stem from circumnutating. As 

 the tracings were made on a vertical glass in front of 

 the plant, it was obviously impossible to trace its 

 course as soon as the leaf became in the evening 

 greatly inclined either upwards or downwards; it 

 must therefore be understood that the broken lines 

 in the diagrams, which represent the evening and 

 nocturnal courses, ought always to be prolonged to a 

 much greater distance, either upwards or downwards, 

 than appears in them. The conclusions which may be 

 deduced from our observations will be given near the 

 end of this chapter. 



In the following list all the genera which include 

 sleeping plants are given, as far as known to us. The 

 same arrangement is followed as in former cases, and 

 the number of the Family is appended. This list 

 possesses some interest, as it shows that the habit of 



