1901 - 2 .] The Functional Inertia of Plant Protoplasm. 201 
The post-stimulant continuance of periodicity of growth or of 
movement — the opening and closing of flowers, movements of 
leaves — whether diurnal or seasonal, is to be credited to this 
property of functional inertia. Thus the periodicity of growth 
induced by the alternation of day and night is retained for a time 
in continuous darkness, and seasonal periodicity is exhibited by 
deciduous trees when removed to countries where the vegetation is 
evergreen, while in cases of experimentally induced periodicity 
(Darwin and Pertz, Annals of Botany , vol. vi. p. 245), the 
periodicity continues for a time after the stimuli are withdrawn. 
All these are examples of the katabolic phase of the inertia. For 
particular cases the time-value of the inertia varies : thus the 
diurnal periodicity is lost after two days by some plants, while it 
is retained for as much as two weeks by others. The latter have 
relatively more inertia than the former. Seasonal periodicity 
exhibits similar variations, and in the practical horticultural 
operations of f forcing ’ and ‘ cold storing,’ we see the property 
under other aspects. In heterauxesis, induced by unilateral stimu- 
lation, by gravity, light or heat, there is a latent period before the 
geotropic, heliotropic or thermotropic curvatures begin to be mani- 
fested. This latent period — that of anabolic inertia — may be 
of any length from a few minutes for geotropism to a few hours 
for thermotropism. In Photomechanical induction (Wortmann, 
Bot. Zeit ., 1883-1885 ; also Lewes, Annals of Botany , vol. xii. 
p. 420), functional inertia takes the form of a physiological insus- 
ceptibility, in that a definite time-exposure to light is necessary to 
produce the maximum effect, and no additional exposure will cause 
the molecules to swing sooner, farther or faster. 
To wound-stimuli, growing as well as adult organs exhibit non- 
responsiveness in varying amount. Thus traumatropic curvature 
in growing roots is only manifested after a latent period — of ana- 
bolic inertia — of an hour or so, and this period may be artificially 
lengthened to as much as eight days (Spalding, Annals of Botany , 
vol. xiii. p. 423). Here, as in other cases, where a sense organ 
has been demonstrated (Czapek’s, Darwin’s, and other experi- 
ments), transmission-time has to be deducted from the latent 
period to get the duration of the anabolic phase. 
Similar evidence is adducible from the researches of Townsend 
