200 Proceedings of Royal Society of Edinburgh. [sess. 
On the Functional Inertia of Plant Protoplasm. By 
R. A. Robertson, M.A., B.Sc., Lecturer on Botany, 
University of St Andrews. Communicated by Dr Fraser 
Harris. 
(Read February 3, 1902.) 
{Abstract.) 
The response by a plant protoplast to an inducing or to an 
inhibitory stimulus is preceded by a period of non-responsiveness, 
and the withdrawal of the stimulus is succeeded by a period of 
continued response or inhibition as the case may be. During 
these intervals, the familiar latent period and period of after- 
effect, or temps de memoir of Massart, the protoplast manifests 
the property of functional inertia (Harris, Brit. Med. Assoc., 
1900), and in the case of the inducing stimulus the two phases 
follow in the order of (1) the Anabolic and (2) the Katabolic, 
while in inhibition the order is reversed. This property is ex- 
hibited by the protoplasm of growing and of adult organs, as well 
as by that of isolated and excised organs ; further, it varies in 
amount and appears under different aspects. 
Taking stimuli and irritabilities in the most general sense 
(Pfeffer, Physiology , p. 11), we have to regard the ordinary growth 
of a plant as a continuous manifestation of irritability in response 
to a particular combination of external stimuli, the so-called tonic 
conditions. These external influences are effective only when 
they operate within definite limits of intensity — the maxima and 
minima. The living molecules have their own rate of vibration, 
and no amount of pushing, i.e., stimulation, will induce them to 
swing faster or farther : they thus exhibit a refractory period, and 
this is one aspect of their functional inertia. A change in one 
or more of the external conditions induces a growth- variation, but 
not all at once ; there is a period of non-responsiveness, of 
accommodation, or of anabolic inertia, and the duration of this 
period varies with the stimulus, e.g., the time-value of the ana- 
bolic inertia is less for a temperature change than for one of the 
oxygen pressure or food supply (Pfeffer, Physiology , p. 512). 
