Associated Stimuli. 
203 
way out of the ground, and that they curve outwards and separate 
on emerging into the light, i.e., that light produces epinastic 
growth. In the tulip, T. gesneriana , the spreading out of the leaves 
which normally occurs in the light, occurs after a time even in 
darkness. Massart points out by the help of other examples, that 
a series can be shown to exist between Ornithogalum and Tulip, in 
which the action of internal stimulation increases. 
Cases like this, in which an action normally occurring as a 
response to a definite stimulus takes place without the stimulus, 
are familiar among periodic phenomena, for instance in the well- 
known case of sleeping plants continuing for a time their rhy¬ 
thmic movement in darkness. 
The phenomena of etiolation are interesting in relation to 
our view of stimulus. Many writers fail to see that the phe¬ 
nomena are of the same nature as more obvious cases of reaction 
to stimulus, and treat them as isolated pathological facts. 
A seed buried in the ground begins its life in darkness and 
normally completes its development when it emerges under the 
changed conditions of illumination. So that if it cannot reach 
the light, it is suffering from the absence of a normal stimulus. 
And since from a biological standpoint, accidentally prolonged 
darkness is a normal occasional event in a plant’s life, we 
should expect adaptations to these conditions. 
Such adaptations do, I believe, occur; in any case it seems to 
me futile to attempt to “explain” a complex set of facts as due 
to disturbed nutrition. In human beings, malnutrition of children 
produces rickets, but the deformity has no tendency to help the 
child to escape from the conditions and is not adaptive. But in 
plants the results, as a whole, are clearly adaptive. 1 
The plant throws its whole energy into elongation, and this 
growth takes place in the parts of the plants which are best adapted 
to escape. In ordinary Dicotyledons we find exaggerated growth of 
the internodes with dwarfing of the leaves, in Cereals and in othei 
Monocotyledons, such as Crocus and Hyacinth, great elongation 
of the leaves. This is easily comprehensible as an adaptation, but 
not as a direct result of malnutrition. Why should want of food 
make a Crocus leaf at the same time long and abnormally narrow ? 
Nor does the direct result of malnutrition explain why for instance 
a Narcissus scape should be greatly elongated in the dark. From 
1 See Godlewski, Biolog. Centralblatt, 1899, and F. Darwin, 
Journal R. Hurt. Soe,, Vol. XIX. 
