324 BOTANICAL GAZETTE [APRIL 
discussing geotropic curvatures, he cites other experiments of Pfeffer, from 
which he concludes that ‘the curving part of the root can contain none of 
the originally irritated cells” (p. 396). These views can hardly be reconciled. 
It seems to be the first induction which is faulty. 
The most notable omission is the absence of any discussion of the theo- 
ries of growth. This could hardly be other than intentional, but surely every 
reader will expect at least a presentation of the current ideas as to the 
mechanics of growth. 
Some details may now be adverted to in order that readers may be guarded 
against indiscriminate acceptance of the author’s statements and definitions. 
It is doubtful whether clearness of ideas is attained by speaking of the 
cell sap as “living matter.’ One might with as much justice include the 
water secreted outside the cell as that secreted within the protoplasm. 
Nor can there be any justification for the association of the phenomena 
of turgor, as in the motor organs of leaves, with those of true growth, under 
the phrase “transitory growth.’’ Greater clarity of conception and one 
sion is secured by limiting the term growth to the permanent or irreversible 
changes of form and volume. The dissociation from growth of certain 
changes (in the interior of spores, etc.) which do not result in increase of 
volume (the author’s sole criterion of growth) is difficult and of doubtful 
value. In fact, it is impracticable to establish a single criterion for growth. 
The account of the causes of twining is quite inadequate, as the author 
does not seem: to be aware of the more recent experiments on the oa 
none since Darwin’s in 1882 being cited. The conclusion generally ) 
today is certainly of that “twining is mechanical — depending Up . 
structure of the stem — rather than responsive ”’ (p. 377)- 
The general discussion of the mechanics of tropic r 
very unsatisfactory. This is partly due, of course, to the pr re 
knowledge, a fact which might well have received more stress than pas 
gives it. The assumptions that are made are too many and too bold ‘ as 
any assistance in clearing up this very difficult subject. For sents 30" ‘a 
relations of growth and turgor are too uncertain at present to ae 
mechanics of phototropism to be explained through the intervention 0 e 
It must first be demonstrated that turgor controls growth, an ries ae 
turgor. Again, the separation of the slow reactions from the et stat 
« differential imbibit 3 
and the latter to “assimilation,” while the ones of intermediate i ner 
probably due to the combined action of assimilation and 
only gratuitous, but absolutely misleading (p. 481). 
does not mean what he says when he suggests that “t 
such a change in the molecules of the curving region as to 
imbibe water with abnormal activity ” (p. 482). 
he tropic age 
cause them © 
