PHYSIOLOGY OF PLANTS. 
S69 
constantly found that a larger quantity of sap flowed from 
the superior, than from the inferior margin of the incision. 
This circumstance led to the opinion, that in the beginning 
of the spring, great quantities of moisture are absorbed 
by trees from the atmosphere, and hence the source of the 
abundance of sap. But this conclusion is found to disagree 
with the phenomena of nature, from the two following 
experiments. 
1. Incisions of various heights being made in the stern of 
several plants, their roots were immersed in a decoction of 
logwood. The roots absorbed the coloured liquor, which at 
length began to flow from the superior, and not from the 
inferior margins of the incisions : nor had the liquor ex- 
tended itself much upwards, beyond the margin of the inci- 
sion from which it was discharged. 
2. In the season when the sap flows most abundantly, 
called the bleeding season, a deep cut was made into the 
branch of a growing vine, and the greatest quantity of sap 
was discharged from the upper margin of the incision ; but 
a branch of the same tree, cut in tile same manner, being 
inverted, the sap flowed most copiously from the other 
margin of the incision, which of course was now that next 
the root. On the other hand, many experiments may be 
brought to prove directly that in the bleeding season” the 
sap ascends from the root towards the branches ; the fol- 
lowing, however, may suffice: 
1. Early in the spring, when little or no sap had as yet 
entered the plant. Dr. Hope made a number of incisions, of 
different altitudes, into the root and stem of a birch. As 
the sap rose, it first flowed from the superior margin of the 
lowest incision, and then, in regular succession, from the 
upper margins of the other incisions, till, at last, it reached 
the highest. 
2. If, in the beginning of the bleeding season, before the 
sap is found in the stem or branches, an incision be made in 
the root of a vine, a considerable flow of sap will follow the 
wound. 
3. The quantity of sap is very generally proportioned to 
the humidity of the soil. 
Of the course of the Succus Pnoritius. When a por- 
tion of the bark and wood of the pine is cut from the stem, 
the succus proprius flows in considerable quantity, both 
from the upper and under margin of the incision. Hence it 
occurred to botanists, that this juice might have little or no 
motion, and that its efflux from such an orifice might depend 
Vor.. II. 3 a 
