204 Proceedings of Royal Society of Edinburgh. [sess. 
acclimatization of plants, artificial production of new varieties of 
bacteria by cultures and variation of external conditions, Stahl’s 
experiments ( Bot . Zeit ., 1884) on plasmodia, and De Tries’ 
researches on biastrepsis of Dipsacus ( Annals of Botany , voi. xiii. 
p. 395). In all these is noticeable the element of time — accom- 
modation to the new conditions — preceding the ultimate response ; 
this represents the time-value of the inertia in respect of the 
particular stimulus. There still remain some interesting cases 
where the inertia amounts to a physiological insusceptibility, and 
where two or more stimuli are required to elicit a manifestation 
of irritability. In this category come the cases of latency described 
by Pierce {Bot. Central ., Bd. 89, 1902, p. 36) and by Terras 
{Trans. Bot. Soc. Edin ., xxi., 1900, p. 318). These lead up to the 
case of the resting seed, which may be regarded as the most 
extreme in this connection. Here at least three stimuli all of a 
tonic character are required to induce a manifestation of irritability. 
The functional inertia of the seed may be said to be infinite in- 
respect of any one of these alone, but relatively small when they 
all act together. Hot only must these stimuli be applied simul- 
taneously, but they must act within definite limits of intensity. 
Any one alone is insufficient to elicit a response, whether applied 
within the limits or far in excess of them. On this point the 
experiments of Brown and Escombe {Roy. Soc. Proc., vol. lxxii. 
p. 161), and of Thiselton-Dyer {Annals of Botany , vol. xiii. 
p. 599), have a distinct bearing. 
Conclusions. 
Plant protoplasm, like animal protoplasm, possesses the property 
of functional inertia. This property finds expression in the 
phenomena underlying the latent period, and temps de memoir 
in the existence of stimulatory limits, in the acquirement, 
maintenance and post-stimulant continuance of periodicity, whether 
diurnal, seasonal or other ; in the phenomena of polarity ; in the 
possession of a limited power of independent activity exhibited 
by isolated organs, protoplasm, and cell organoids. On it as one 
factor depend the possibility of educating protoplasm and the 
acquirement of new characters as seen in nature, and also the 
results of experiment. 
[Issued separately June 9 , 1902 .) 
