[ 3 ° ] 
PHYSIOLOGICAL STUDIES IN PLANT 
ANATOMY 
VI. ETIOLATION 
By J. H. PRIESTLEY and J. EWING 
CONTENTS 
PAGE 
Introduction ........ 30 
Experimental Study of Etiolation . . . . 31 
Discussion 
(1) The Etiolated Leaf . . . . . . 37 
(2) The Etiolated Stem . . . . . 38 
Summary ........ 42 
References ........ 43 
Introduction 
T he complex phenomena of plant growth may be regarded as a 
dynamic equilibrium between the internal tendencies inherited 
by the plant and the external factors operating during its develop¬ 
ment. If this conception be applied to the analysis of the Angiosperm 
seedling given in the first paper of the series ( 15 ), in which it was 
described as an axis capped by two opposing, differently constituted, 
apical meristems with an equatorial region of food supply, the 
question immediately arises as to what extent external factors influ¬ 
ence the subsequent development of the seedling. It is evident that 
normally the two apical meristems continue their growth under very 
different conditions, the stem meristem rising into the light and into 
comparatively dry air, the root meristem continuing its growth in 
darkness and in a moist atmosphere. The investigator has to hand 
experimental methods which will enable him to ascertain whether 
the characteristic behaviour of these different meristems is inseparably 
associated with the natural environment; and such experiments 
have frequently been carried out. The problem requires consideration 
anew from the standpoint adopted in these papers, and the results 
of some such experiments will now be considered. Few new observa¬ 
tions fall to be recorded, but as the standpoint from which the facts 
are analysed is all important it seems desirable to make this clear by 
a discussion of our own experiments before attempting any discussion 
of earlier work. 
The experimental results requiring discussion are those obtained 
when a stem apex is allowed to develop in darkness, when the charac- 
