PRESSURE OF SAP. 



195 



Gk APE- Vine. 



changes in the meteorological conditions in general, as well as by the al- 

 ternations of day and night. The fluctuations in the birch are very de- 

 cided early in May, when the leaves are expanding, while those in the 

 grape-vine are very slight at any tune, except as the mercury steadily 

 rises to its maximum for the season and then as steadily declines. 



Many more observations upon the different species are desirable before 

 attemi^ting to speculate concerning these remarkable phenomena, but 

 these few data will sei-ve as a beginning for more complete investi- 

 gations. 



