FUNCTION.] HALES ON PERSPIEATION. 291 



velocities will be 4 : 3 : : 45^ : 34. But if we suppose the 

 pores in the surface of the leaves to bear the same proportion, 

 as the area of the sap vessels in the stem do to the area of the 

 stem, then the velocity, both in the leaves, root, and stem, 

 will be increased in the same proportion. 



" From July 3rd to August 3rd. I weighed, for nine several 

 mornings and evenings, a middle-sized Cabbage plant, which 

 grew in a garden-pot, and was prepared with a leaden cover, 

 as the Sunflower. Experiment 1st. Its greatest perspiration 

 in twelve hours' day, was 1 pound 9 ounces ; its middle per- 

 spiration 1 pound 3 ounces = 32 cubic inches. Its surface 

 2736 square inches, or 19 square feet. Whence dividing the 

 32 cubic inches by 2736 square inches, it will be found that 

 a little more than the -$ of an inch depth perspires off its 

 surface in twelve hours' day. The area of the middle of the 

 Cabbage stem is -f-- of a square inch ; hence the velocity of 

 the sap in the stem, is to the velocity of the perspiring sap, 

 on the surface of the leaves, as 2736 : -HHf : : 4268 : 1. for 

 2 ^x_i6 _ 4268> But if an a n owance i s to be made for the 



solid parts of the stem, (by which the passage is narrowed,) 

 the velocity will be proportionably increased. The length of 

 all its roots 470 feet, their periphery at a medium of an 

 inch, hence their area will be 256 square inches nearly ; 

 which being so small, in proportion to the area of the leaves, 

 the sap must go with near eleven times the velocity through 

 the surface of the roots, that it does through the surface of 

 the leaves. And setting the roots at a medium at twelve 

 inches long, they must occupy a hemisphere of earth two 

 feet diameter, that is, 2-1 cubic feet of earth. By comparing 

 the surfaces of the roots of plants, with the surface of the 

 same plant above ground, we see the necessity of cutting off 

 many branches from a transplanted tree; for, if 256 square 

 inches of root in surface was necessary to maintain this 

 Cabbage in a healthy natural state, suppose, upon digging it 

 up, in order to transplant, half the roots be cut off (which is 

 the case of most young transplanted trees), then it is plain 

 that but half the usual nourishment can be carried up through 

 the roots on that account ; and a very much less proportion 

 on account of the small hemisphere of earth the new planted 



