THE EEASON WHY. 297 



"Then shall the earth yield her increase; and God, even our own God, shall 

 bless us." PSALM; XLVII. 



1177. Why have the berries of the mistletoe a thick viscid 

 juice ? 



Because the mistletoe is a parasitical plant, growing upon the 

 bark of other trees. It will not grow in the ground ; its seeds are 

 therefore filled with an exceedingly sticky substance, which serves to 

 attach them to the bark of trees, to which the berries attach them- 

 selves at once, by throwing out tough fibres ; and the next year the 

 plant grows. 



Fig. 75. THE MISTLETOE. 



1178. Sow are the seeds of the mistletoe transferred from 

 its own stem to the bark of trees. 



Various birds, and particularly the missel thrush, feed upon the 

 berries. As the bird moves in pursuit of its food, the viscid berries 

 attach themselves to its feathers, and in this way the thrush is the 

 instrument which conveys the seed to the spot to which it adheres, 

 and from which the tree ultimately grows. 



1179. What is the circulation of the sap in plants ? 



The circulation of the sap is the movement of the nutritive juices 

 by which the plant is sustained. There is a slow uninterrupted 

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