t on
a growing root to the action of the same cause on a thermometer {118b}
was a quite satisfactory proceeding. And there are many other passages
in _Vegetable Staticks_ where one feels that his speculations are too
heavy for his knowledge.

Something must be said of Hales' relation to his predecessors and
successors in botanical work. The most striking of his immediate
predecessors were Malpighi 1628-1694, Grew 1628-1711, Ray 1627-1705, and
Mariotte (birth unknown, died 1684); and of these the three first were
born one hundred years before the publication of _Vegetable Staticks_.
Malpighi and Grew were essentially plant-anatomists, though both dealt in
physiological speculations. Their works were known to Hales, but they do
not seem to have influenced him.

We have seen that as a chemist Hales is somewhat of a solitary figure,
standing between what may be called the periods of Boyle and of
Cavendish. This is even more striking in his botanical position, for
here he stands in the solitude of all great original inquirers. We must
go back to Van Helmont, 1577-1644, to find anyone comparable to him as an
experimentalist. His successors have discovered much that was hidden
from him; but consciously or unconsciously they have all learned from him
the true method and spirit of physiological work.

It may be urged that in exalting Hales I am unfair to Malpighi. It may
be fairer to follow Sachs in linking these great men together, and to
insist on the wonderful fact that before Malpighi's book in 1671,
vegetable physiology was still where Aristotle left it, whereas 56 years
later, in 1727, we find in Hales' book an experimental science in the
modern sense.

It should not be forgotten that students of animal physiology agree with
botanists as to Hales' greatness. A writer in the _Encyclopaedia
Britannica_ speaks of him as "the true founder of the modern experimental
method in physiology."

According to Sachs, Ray made some interesting observations on the
transmission of water, but on the whole what he says on this subject is
not important. There is no evidence that Ray influenced Hales.

Mariotte, the physicist, came to one physiological conclusion of great
weight; {119} namely, that the different qualities of plants, _e.g._
taste, odour, etc., do not depend on the absorption from the soil of
differently scented or flavoured principles, as the Aristotelians
imagined, but on _specific differences_ in the way in w