SECT. II. ASCENT OF THE SAP. 103 



way, and others made to bleed copiously ; but the 

 latter were afterwards as vigorous and productive as 

 the former. The American Maple will also con- 

 tinue to yield its usual quantity of sap in the spring 

 for many years ; though it requires now and then 

 an interval of rest. 



The plant always bleeds most freely about the Which is 

 time of the opening of the bud ; for in proportion per 

 as the leaves expand the sap flows less copiously, 

 and when they are fully expanded it entirely ceases. 

 But this suspension is only temporary, for the plant 

 may be made to bleed again in the end of the 

 autumn, at least under certain conditions. If an 

 incision is now made into the body of the tree 

 after the occurrence of a short but sharp frost, when 

 the heat of the sun or mildness of the air begins to 

 produce a thaw, the sap will again flow. It will 

 flow even where the tree has been but partially 

 thawed, which sometimes happens on the south 

 side of a tree, when the heat of the sun is strong 

 and the wind northerly. At the seasons now speci- 

 fied, therefore, the sap is evidently in motion ; but 

 the plant will not bleed at any other season of the 

 year. Are we to conclude, therefore, that the Though 

 motion of the sap is at such other season wholly motion "is 

 suspended ; or that it only flows with diminished J^ r 

 velocity ? It has been the opinion of some phyto- suspended, 

 logists, indeed, that the motion of the sap is wholly 

 suspended during the winter. But though the 

 great cold of winter, as well as the great heat of 



