Prop-Roots of the Laburnum. 
BY 
A. W. BORTHWICK, Sc.D. 
With Plate XXIV. 
In certain trees, such as the mangrove and screw-pine, as 
well as in lower-growing plants like species of Sty/idium, the 
production of prop-roots has become a fixed characteristic 
feature. In the case of the tree forms mentioned, the prop-roots 
give the tree a much broader base and more points of attach- 
ment to the soft, slimy mud in which it grows, and they also 
form supporting buttresses which are better able than a single 
thick trunk to withstand the strain and stress of wind an 
waves. We have here an example of special adaptation to 
environment. When the tap-root and stem-base begin to decay 
they are replaced by the prop-roots. It is striking to find much 
the same kind of thing taking place in certain forest trees, 
where a damaged root-system is often made up for by the 
formation of adventitious roots around the stem-base. In some 
cases strong adventitious roots are produced at a considerable 
height from the ground; this may occasionally be seen in 
Robinia Pseudacacia. A few years ago a tree of this species 
near Edinburgh was blown down; the lower part of the trunk 
and root-system had been very much decayed, and after the fall 
there remained standing a strong adventitious root which had 
been produced in the neighbourhood of a cut-off branch some 
12 or 14 feet from the ground. This root had grown down 
hidden from view between the bark and wood, which was 
totally decayed on one side of the trunk. On the sounder parts 
of the stem, at varying distances from the ground, several similar 
[Notes, R.B.G., Edin., No. XVIII., August 1907.] 
