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PHYSIOLOGICAL STUDIES IN PLANT 
ANATOMY 
V. CAUSAL FACTORS IN CORK FORMATION 
By J. H. PRIESTLEY and LETTICE M. WOFFENDEN 
CONTENTS 
PAGE 
Introduction ..... 252 
I. The Formation of Wound Cork . 253 
II. Leaf Fall ...... 261 
III. Normal Cork and Lenticel Formation 262 
Summary ...... 266 
References ..... 267 
Introduction 
W e propose to attempt in this paper a reconsideration of the 
phenomena connected with cork formation under the various 
conditions in which it is known to occur within the plant. The 
attempt will involve the brief re-statement of the results of many- 
other investigators, but this repetition seems worth while as it is 
hoped to show that in every case, the formation of cork follows from 
certain causally connected phenomena, a sequence of causation 
which so far as we are aware has not been traced previously. 
We have been led to examine cork formation from this point of 
view as the result of other work which was proceeding in the 
laboratory, and which began with a study of the mechanism of sap 
exudation in the phenomenon of root pressure ( 19 ). A wider extension 
of the investigation has shown that sap pressures may arise within 
the vascular strands as the result of the activity of parenchymatous 
tissues in root, stem or leaf(2i). At the same time other observa¬ 
tions ( 23 , 24 ) have directed attention to the importance of this sap 
pressure in initiating and sustaining the activity of meristematic 
tissues. Such tissues are always parenchymatous tissues irrigated by 
the sap from the vascular strand. This sap supply is in many cases 
controlled and contained by the limiting cylinder of the endodermis 
(Priestley and North (22)), and in such cases the meristematic activity 
of parenchymatous tissues external to the endodermis may be 
strictly limited. 
When we apply these considerations to the case of cork formation 
we are dealing with the origin of a tissue which arises from the 
