s to a height of 4+34 or 136
inches, or in one hour to 28.3 cm. {126d} This is a result comparable
to, though very much smaller than, Sachs' result with the sunflower, viz.
63 cm. per hour.

The data are however hardly worth treating in this manner. But it is of
historic interest to note that when Sachs was at work on his
_Pflanzenphysiologie_, published in 1865, he was compelled to go back
nearly 140 years to find any results with which he could compare his own.

We need not follow Hales into his comparison between the "perspiration"
of the sunflower and that of a man, nor into his other transpiration
experiments on the cabbage, vine, apple, etc. But one or two points must
be noted. He found {127a} the "middle rate of perspiration" of a
sunflower in 12 hours of daylight to be 20 ounces, and that of a "dry
warm night" about 3 ounces; thus the day transpiration was roughly seven
times the nocturnal rate. This difference may be accounted for by the
closure of the stomata at night, a phenomenon unknown to Hales.

Hales {127b} notes another point which a knowledge of stomatal behaviour
might have explained, viz., that with "scanty watering the perspiration
much abated"; he does not attempt an explanation, but merely refers to it
as a "healthy latitude of perspiration in this sunflower."

In the course of his work on sunflowers he notices that the flower
follows the sun. He says, however that it is "not by turning round with
the sun," _i.e._ that it is not a twisting of the stalk, and goes on to
call it _nutation_, which must be the _locus classicus_ for the term used
in this sense.

An experiment {128a} that I do not remember to have seen quoted elsewhere
is worth describing. It is incidentally of interest as showing the
generous scale on which his work was planned. An apple bough five feet
long was fixed to a vertical glass tube nine feet long. The tube being
above and the branch hanging below, the pressure of the column of water
would act in concert with the suck of the transpiring leaves, instead of
in opposition to this force. He then cut the bare stem of his branch in
two, placing the apical half of the specimen (bearing side branches and
leaves) with its cut end in a glass vessel of water; the basal and
leafless half of the branch remained attached to the vertical tube of
water. In the next 30 hours only 6 ounces dripped through the leafless
branch, whereas the leafy branch absorbed 18 ounces. This, as