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culation, or at least constant supply of sap, 

 we must consider that boughs even of con- 

 siderable thickness, cut off in the autumn, 

 will become dried throughout before the 

 spring. But what can account for the 

 moisture of boughs, and even the most 

 delicate spray, exposed at great heights in 

 the air, but the constant supply of sap ? 



Indeed, if the first theory were correct, 

 there is no reason why plants should not 

 live through the winter out of the ground, 

 and plants taken up in the autumn should 

 grow as freely when again put in in the 

 spring as if they had just been taken up. 

 The contrary of this is the case ; the roots 

 of plants taken up in the autumn, as well 

 as the plants themselves, soon become 

 dry. Why ? Because the roots are deprived 

 of the power of imbibing moisture. 



I have observed that if the stem of 

 a young tree grown in water is cut at the 

 beginning of winter, the root immediately 

 ceases to grow; doubtless because the atem 



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