PROCEEDINGS 
OF THE 
ROYAL SOCIETY OF EDINBURGH. 
VOL. XLI. 1920-21. 
I. — Size, A Neglected Factor in Stelar Morphology. Opening 
Address by Professor F. O. Bower, M.A., D.Sc., LL.D., 
F.R.S., F.L.S., President. 
(Read October 25, 1920. MS. received November 1, 1920.) 
The principle of similar structures was first enunciated by Galileo. 
Applying it mechanically, it appears that the strength of a structure varies 
as the square of the linear dimensions, and the weight as the cube. This 
principle and its mechanical applications have been widely illustrated 
by reference to the bodies of animals, and many of their peculiarities are 
necessary consequences of its effect in the course of their evolution. For 
instance, the columnar legs of the elephant or of the moa are held to be the 
inevitable sequel to the large size and consequent weight of those animals, 
while the thin arched legs of insects are only possible where the body 
itself is small and light. Such questions have been adequately dealt with 
in D’Arcy Thompson s book on Growth and Form. Botanists have, how- 
ever, been slower in applying the principle to the study of plants. It 
is true that the question of the practicable limit of size of trees has long 
ago been discussed from this point of view, and it is recognised that a 
change either of material or of method of construction would be necessary 
for effective growth beyond the limits already reached by some of the 
largest of them. In fact, that about 300 feet is the extreme height that 
can be self-supporting with the usual type of construction of the trunk. 
But the principle is also applicable to other points of construction, such 
as the size and constitution of individual cells, and even to the forms 
of chloroplast : as well as to various problems of distribution of tissue- 
VOL. XLI. ' 1 
