244 DARWIN—A BOTANICAL PHYSIOLOGIST. 
ofa mirror, from below, and not otherwise, direct their stems 
towards the earth and their radicles towards the sky.” But this 
discovery seems to have been generally overlooked, though it is 
mentioned in Treviranus’ Physzologze. 
Among the remaining diagrams, the most interesting are 
those which give the result of Hope’s investigation of the distri- 
bution of longitudinal growth in stems. In this he was 
probably following Hales,!. who marked both leaves and stems 
at regular intervals, which being remeasured gave the desired 
result. As far as stems are concerned Hales’ method is not nearly 
so good as that of Hope. Hales marked a vine shoot in the spring 
and only remeasured it in September. Hope marked the young 
shoots of trees and of a hop and measnred the increase of each 
zone at intervals of either one or two days. If he had persevered 
he would certainly have made out the laws of the distribution of 
growth which we owe to Sachs. But he seems to have been 
careless in measuring the marked zones, and though he notes 
as remarkable that the quickest growth was not necessarily 
in the zone nearest the apex, there is no evidence that he had 
mastered the problem: his observations and the diagrams in 
which they are embodied are hardly worth reproducing. In 
his 7S. Lectures (p. 50) he draws the interesting conclusion 
“that stems do not elongate exactly as roots do (according to 
Mr. Du Hamel), but that they elongate not only at the extremity 
but even in the part near it.” This generalisation is an approxi- 
mation to Sachs’ teaching on the subject. 
Hope also made experiments on the “descent of sap” by the 
well-known methods of “ringing” and of compression by means 
of ligatures. His diagrams are records of actual experiments, 
but they are hardly worth giving, since both Hales and Du Hamel 
had previously published drawings illustrating this method of 
inquiry, Nor does it seem necessary to reproduce Hope’s 
records of the healing of injured tree-trunks, though they are 
not without a certain interest. 
* Vegetable Staticks, 1727, p. 330. 
