btain
nourishment, not only from the earth, "but also more sublimed and exalted
food from the air, that wonderful fluid, which is of such importance to
the life of Vegetables and Animals," etc. We shall see that his later
statement is not so definite, and it is well to rescue this downright
assertion from oblivion.

His book begins with the research for which he is best known, namely that
on transpiration. He took a sunflower growing in a flowerpot, covering
the surface of the earth with a plate of thin milled lead, and cemented
it so that no vapour could pass, leaving a corked hole to allow of the
plant being watered. He did not take steps to prevent loss through the
pot, but at the end of the experiment cut off the plant, cemented the
stump, and found that the "unglazed porous pot" perspired 2 ozs. in 12
hours, and for this he made due allowance.

The plant so prepared he proceeded to weigh at stated intervals. He
obtained the area of the leaves by dividing them into parcels according
to their several sizes, and measuring one leaf {125} of each parcel. The
loss of water in 12 hours converted to the metric system is 1.3 c.c. per
100 sq. cm. of leaf-surface; and this is of the same order of magnitude
as Sachs' result, {126a} namely, 2.2 c.c. per 100 sq. cm.

He goes on to measure the surface of the roots {126b} and to estimate the
rate of absorption per area. The calculation is of no value, since he
did not know how small a part of the roots is absorbent, nor how
enormously the surface of that part is increased by the presence of
root-hairs. He goes on to estimate the rate of the flow of water up the
stem; this would be 34 cubic inches in 12 hours if the stem (which was
one square inch in section) were a hollow tube. He then allowed a
sunflower stem to wither and to become completely dry, and found that it
had lost .75 of its weight, and assuming that the .25 of the "solid
parts" left was useless for the transmission of water he increases his 34
by 1/3 and gives 45-1/3 cubic inches in 12 hours as the rate. But the
solid matter which he neglected contained the vessels, and he would have
been nearer to the truth had he corrected his figures on this basis. The
simplest plan is to compare his results with those obtained by Sachs
{126c} in allowing plants to absorb solutions of lithium-salts. If the
flow takes place through conduits equivalent to a quarter of a square
inch in area, the fluid will rise in 12 hour