ETIOLATION AS A PHENOMENON OF ADAPTATION. 347 
too wide and too complex for discussion in the present form. 
The point which I wish to emphasise is that with our present 
knowledge no theory of etiolation based on disturbed nutrition 
as a cause can possibly explain the observed facts. Take, for in- 
stance, Sachs's * theory, according to which the cause of etiolation 
is the absence of certain unknown formative materials, which can 
only be manufactured in green leaves in light. How is such a 
theory as this to explain the fundamental fact that the leaves 
of cereals and other monocotyledons become abnormally long 
though narrow in darkness ? It would be necessary to invent 
more hypotheses — for instance, that the material required for 
growth in length can be manufactured without light, whereas 
the material for growth in breadth cannot so be manufactured. 
The same general objection holds against any nutrition theory of 
etiolation : that though disturbed nutrition can be conceived as 
producing deformity in general, we cannot at present see how it 
can produce the diverse types of deformity which we know to 
exist. 
Almost everyone who has written on etiolation has treated it 
as a disease or pathological condition without attempting to 
correlate the particular abnormality with the biology of the 
normal plant. 
As far as I know, Godlewski t is the only writer who has 
frankly taken the opposite view.J I agree with him in believing 
that etiolation is a phenomenon of adaptation, in which the 
particular deformity due to changed environment is of necessity 
correlated with the character of normal growth. The difference 
between the commonly received view (which I may call the 
nutrition theory) and that of Godlewski § (the adaptation iYieovy) 
may be made clear by an illustration from the domain of human 
deformity. Rickets may be induced by feeding an infant, too 
* Vorlesungen, 1882, p. 647. 
f Biolog. : Centralblatt, Oct. 15, 1889. Godlewski, however, points out 
that a similar idea was formulated by Boehm in a popular work, Die 
Ndhrstoffe der Pflanzc, 1886. 
J Sachs shows, however, a tendency to this view in his classical paper, 
Bot. Zeitung, 1863. 
§ In Godlewski's interesting paper the author confines himself to the 
consideration of the main facts exhibited by etiolated plants, i.e: the 
increased internodal growth and dwarfed leaves of the dicotyledonous stem, 
and the elongated narrow leaves of the monocotyledons. He is not to be 
held responsible for the speculations on other aspects of the case contained 
in the present paper. 
B 2 
