CHAPTER XV 



THE SLEEP OF PLANTS 



DIFFERENT organs of plants are in a state of constant 

 movement which is not immediately noticeable. But a 

 striking change is observed in their respective positions 

 at day and night. The explanation of this particular 

 phenomenon of Nyctitropism has hitherto proved very 

 baffling, as will be seen from the following summary given 

 by Jost in his ' Physiology of Plants/ 



Many plant organs, especially foliage and floral leaves, take 

 up towards evening positions other than those they occupy by 

 day. Petals and perianth leaves, for example, bend outwards 

 by day so as to open the flower, and inwards at night so as to 

 close it. ... Many foliage leaves also may be said to exhibit 

 opening and closing movements, not merely when they open and 

 close in the bud, but also when arranged in pairs on an axis they 

 exhibit movements towards and away from each other. In 

 otru cases, speaking generally, we may employ the terms 

 night-position and day-position for the closed and open con- 

 ditions respectively. The night-position may also be described 

 as the sleep-position. ... A completely satisfactory theory of 

 nyctitropic movements is not yet forthcoming. Such a theory 

 can only be established after new and exhaustive experimental 

 research. 



Bose has recently carried out a complete investigation 

 on the subject, the results of which are given in Vol. II of 

 the 'Transactions of the Bose Institute/ Without enter- 

 ing into details, it may be said that the new advance 

 here consists in distinguishing for a series of simple 



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