338 THE SLEEP OF LEA.VES. 



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 tlie plants as well. Most botanists now be- 

 lieve that odor and ^howy 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 tliis 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 bum])le 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 diiferent positions at night from those assumed during 

 the day time. 



This difference in position is caused 

 by turgescence in the pHlvinus, which is 

 the name given to a mass of small cells 

 of a j)ale color found in a certain portion 



Fig. lSO.^Trif(>liumrcpen>< : 

 a, leaf during the day ; /(.leaf of the leaf Stalk. 

 asleep ai 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 jmrpose tluit 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 incessalit motion, 

 circumnutating. Tlie sleep of plants is a mere modified form of 

 t'.'.l.: universal circumnutation. 



