Associated Stimuli. 
205 
exposure to light in the absence of CO„ are not etiolated, 1 here the 
stimulus of light is enough without the stimulus of nutrition. 
I am inclined to think that a form of etiolation produced by 
damp air is a case of associated engrams. Certain rosette-leaved 
plants do not retain their characteristic form in darkness, hut spindle 
out into a shoot, and in some—not all—of these, the same effect 
may be brought about by exposing them to damp air in light. 2 
This must, I think, depend on the fact that dampness and darkness 
occur together in nature, e.g. under ground, and in a less marked 
degree under heaps of dead lea ves or other debris. The occurrence 
of this form of etiolation is capricious, thus Plantago gives no such 
reaction, Sempervivum reacts to both darkness and damp air, 
Capsella to damp air but not to darkness. 
Finally, I must add, that I do not pretend to be able to explain 
thew hole of the facts of etiolation, which have only been introduced 
to illustrate a possible case of associated engrams. 
The association of stimuli accounts, as Semon suggests, for 
many of the curious cases known as change in “ Stimmung ” 
i.e. disposition or tone. 
The spores of certain Ferns do not normally germinate in 
darkness, 3 but by a temperature of 32°C they can be made to 
germinate in the dark. To say that these are cases of change in 
tone is to re-state the fact in other words, but if we may look 
on them as due to associated engrams we at least classify them 
with a large group of phenomena. 
I should suppose that light and warmth generally occur together, 
and that an act carried out at the suggestion of illumination 
would generally occur simultaneously with raised temperature. 
Therefore the engrams of heat and light would come to be 
associated, and accordingly it is conceivable that heat alone should 
produce the effect normally due to light and heat. 
In considering the periodic movements of sleeping plants, we 
shall see that there is some evidence of heat producing the effect 
normally due to light. 
I have a few words to say on the adaptive character of plant 
reactions. Even those who look on adaptation as an abomination 
of desolation, standing where it ought not, cannot deny the fact 
that the outcome of reactions to stimuli is, broadly speaking, 
1 In other cases serious disturbances to growth are produced by 
these conditions. 
2 Wiesner, Ber. Deutsch. Bot. Ges. IX., 1891. 
3 Pfeffer’s Physiologie, II., p. 105. 
