Review : 
35 6 
cannot help feeling that if selection must be made, the place of 
honour should be allotted to the colloidal organisation of protoplasm, 
whereby a stable vital machinery is built up on a basis of some 5% 
of solid matter and 95% of water. It is rather surprising to note 
that the word “colloid ” nowhere occurs in this physiology. 
Another aspect of the relation of the plant to water, on which 
Barnes is strongly partisan, is the question of the significance of 
transpiration. Is it of profound biological advantage and the plant- 
structure adapted to promote it, or is it a necessary evil of the 
environment in which land plants grow—the last infirmity of 
noblest vegetation ? To the best of the reviewer’s knowledge, 
though various distinguished workers have held the latter view, this 
is the only text-book that puts aside resolutely the evidence for the 
former, and is content to teach its students only the latter in its 
entirety. On p. 326 we read “ Transpiration, far from being a function 
of plants, is an unavoidable danger.” This view is elaborated at 
some length and is in striking contrast with the statement in the 
Bonn Text-book, mostly read by our undergraduates, where we read 
“ Were transpiration not in the highest degree useful and even 
necessary for the acquisition of mineral substances, provision would 
certainly have been made by plants to restrict it within the narrowest 
possible limits” (p. 197). 
It is not easy to argue wisely about what is or is not, on the 
whole, an advantage to the plant. What we really lack is critical 
experimentation on the growth of ordinary mesophytes when trans¬ 
piration is reduced nearly to zero. This only requires experiment 
on a properly large and expensive scale, and what one would have 
admired most in an American text-book would have been a statement 
that we are ignorant on this fundamental point and an appeal that 
$5,000 spent on special constructions would certainly provide the 
answer. 
The reason that Barnes gives for the faith that is in him is 
that “ it is impossible to reconcile with present ideas of osmotic 
movement ” the conception of a transpiration current sweeping in 
needful mineral salts from outside the roots. Pure water he admits 
it may sweep in, to replace water lost in leaf-evaporation, but the 
dilute salts outside cannot be drawn in through the root-cortex 
against the stronger concentration of salts within the plant. We 
see that the bases of his objections are not so much definite 
experiments as human ignorance (note the words we have italicised). 
A connecting factor undervalued by those who hold with 
