262 
LOCK : THE GROWTH OF 
studied likewise by Baranetzky who attributed the periodicity 
in this case also to the action of the alternating changes of 
light and darkness. The root pressure maximum occurs 
usually in the afternoon. At this time Kraus* found the 
volume and turgour pressure of the cortex of woody branches 
to be at a minimum, the minimum amount of water being 
then present in the cortical cells. It seems probable that the 
increased transpiration by day may afford a rational explana¬ 
tion of both these phenomena as well as of others. 
For these reasons I would submit that the question requires 
further examination whether the daily periodicity so widely 
observed in the functions of plants may not be partly or even 
largely determined in a considerable number of cases by 
periodic changes in the psychrometric condition of the 
atmosphere, and whether the influence of the daily alterations 
of light and darkness may not have been somewhat 
exaggerated. 
Q—The Mechanism of the Effect of Moisture. 
6. Baranetzkyf suggested that the periodic after-effect of 
light was due to the existence of an 4 elastic reaction ’ in the 
plant. The effect of the stimulus of darkness was to increase 
the rate of growth up to the limit of 4 elastic stretching,’ and 
this was followed by a series of oscillations of opposite phases 
until equilibrium had been restored. The differences in 
length of the periods of oscillation which were observed in 
different cases were regarded by Baranetzky as being due to 
differences in the amount of energy which had been 
imparted in starting the oscillations. If this is the case it 
is plain that there can be no true analogy with any purely 
mechanical action ; the periodicity must be essentially a vital 
phenomenon. 
Godlewski J from the sudden and temporary nature of the 
response to a change of atmospheric moisture in the case of 
* Loc. cit. p. 45. 
t Loc. cit., p. 14. 
J Anzeiger d. Akad. d. Wissenschaften in Krakau. 1890. p. 292. 
