PRESSURE OF SAP. 187 



with regularly increasiug amounts till they reached the 

 maximum of about fifteen pounds from one spout per diem 

 for each species. This was the last of April, soon after 

 Avhich the leaves began to expand tind the flow to diminish. 



The hornbeam did not flow when tapped April 21st, but 

 on the first of May bled about ten pounds of nearly tasteless, 

 turbid sap. On the third of May, it reached its maximum of 

 twelve pounds and six ounces from one spout, and slowly 

 declined in amount after this date. 



The wild vine afforded from a single spout eight ounces of 

 nearly tasteless, limpid sap. May 26th, which was the largest 

 amount for any one day, and bled through the entire month of 

 May a few ounces daily. 



It only remains to state in a few words some of the surpris- 

 ing results obtained by the application of mercurial gauges to 

 the sugar-maple, the black birch and the grape-vine. Obser- 

 vations were made on one or more gauges several times daily 

 and occasionally every hour of the day and night, from the 

 first of April to the 20th of July. 



A gauge was attached to a sugar-maple March 31st, 

 which was three days after the maximum flow of sap for this 

 species, so that further observations are required earlier in 

 the season to complete the record and determine with certainty 

 the maximum pressure which it exhibits in spring. Of the 

 record made, the following facts are specially interesting. 

 First, the mercury was subject to constant and singular oscil- 

 lations, standing usually in the morning below zero, so that 

 there was indicated a powerful suction into the tree, and ris- 

 ing rapidly with the sun until the force indicated was suffi- 

 cient to sustain a column of water many feet in height. Thus 

 at 6, A. M., April 21st, there was a suction into the tree sujffi- 

 cient to raise a column of water 25.95 feet. As soon as the 

 morning sun shone upon the tree the mercury suddenly began 

 to rise, so that at 8.15, a. m., the pressure outward was 

 enough to sustain a column of water 18.47 feet in height, a 

 change represented by more than 44 feet of water. On the 

 morning of April 2 2d the change was still greater, requiring 

 for its representation 47.42 feet of water. These extraordi- 

 nary fluctuations were not attended by any peculiar state of 



