328 THE SLEEP OF LEAVES. 



many persons on a great variety of plants show results quite as 

 remarkable as those above cited. 



Here the bees and bumble bees not only make use of a waste 

 product, but help the plants as well. Most botanists now be- 

 lieve that odor and showy flowers are advertisements for attract- 

 ing insects; and that nectar and surplus pollen are the wages to 

 compensate insects for services rendered in fertilization. 



If this be the case should not the farmer seek to encourage 

 meadow mice, which make the nests sought by bumble bees in 

 which to rear their young. The bumble bees, at least, should be 

 encouraged. It is not improbable that the time may come 

 when queen bumble bees will be reared, bought and sold for 

 their benefit to the crop of clover seed. 



The Sleep of Leaves. This can in no way be compared with 

 the sleep of animals, but refers to the fact that the leaves of clo- 

 vers take different positions at night from those assumed during 

 the day time. 



This difference in position is caused 

 by turgescence in the pulvinus, which is 

 the name given to a mass of small cells 

 of a pale color found in a certain portion 



, leaf during the day ; 7>, leaf o f the leaf stalk, 

 i night. 



FIG. 13Q.Trifoliumrei>en>s ; 

 , leaf during the day ; 7), lei " 

 asleep at night. (Darwin.) 



Experiments show that leaves kept open or spread apart con- 

 tain more dew in the morning, and hence become cooler than 

 those which approach each other. The leaves crowd together, 

 or "sleep," for the same purpose that pigs crowd together in 

 cold weather, viz : to keep warm. It has been found that the 

 leaves which sleep do not remain quiet during the night, but 

 continue, without exception, to move during the whole twenty- 

 four hours. All non-sleeping leaves are also in incessant motion, 

 circum nutating. The sleep of plants is a mere modified form of 

 this universal circumnutation. 



