Physiological Studies in Plant Anatomy 61 
vascular cylinder from the base to within a few millimetres of the 
growing point. It is shown that the presence of this endodermis, 
restricting the flow of sap which normally irrigates the cortex, 
explains many of the morphological and structural peculiarities 
exhibited by these particular plants under etiolation conditions. 
In conclusion the writer would like to make certain acknow¬ 
ledgements; firstly to the many other workers in the Botanical 
Department at Leeds, both staff and students, whose names are 
not associated with the papers published below, but whose active 
cooperation has been freely given and fully utilised throughout. 
Secondly, whilst slowly developing the theory of the significance 
of sap movement to growth, the writer is very conscious that his 
views have been partly inspired by the suggestive experiments and 
writings of Jacques Loeb. His papers, cited below(2), have a general 
relation to the present line of thought, although these investigations 
have developed quite independently, and specific reference to Loeb’s 
work has seldom proved necessary when setting down the results 
contained in the subsequent papers in this series. 
Further Papers in the series, to appear in this Journal. 
II. The Physiological Relation of the Surrounding Tissue to the 
Xylem and its Contents. J. H. Priestley and Dorothy Armstead. 
III. The Structure of the Endodermis in Relation to its Function. 
J. H. Priestley and Edith E. North. 
IV. The Water Relations of the Plant Growing-Point. J. H. 
Priestley and R. M. Tupper-Carey. 
V. Causal Factors in Cork Formation. J. H. Priestley and 
Lettice M. Woffenden. 
VI. Etiolation. J. H. Priestley and J. Ewing. 
REFERENCES 
(1) Lang, W. H. A Theory of Alternation of Generations in Archegoniate 
Plants based upon the Ontogeny. New Phytol. 8, pp. 1-12. 1909. 
- Presidential Address, Section K. British Association Report, Man¬ 
chester. 1915. 
(2) Loeb, Jacques. Rules and Mechanism of Inhibition and Correlation in 
Regeneration of Bryophyllum Calycinum. Bot. Gaz. 60 , p. 249. 1915. 
- Law Controlling the Quantity of Regeneration in the Stem of Bryo¬ 
phyllum Calycinum. Journ. Gen. Physiol. 1 , p. 81. 1919. 
- Quantitative Laws in Regeneration. I. Journ. Gen. Physiol. 2, 
p. 297. 1920. 
- Quantitative Laws in Regeneration. II. Journ. Gen. Physiol. 2, 
p. 651. 1920. 
-Physiological Basis of Polarity. I. Journ. Gen. Physiol. 1, p. 337. 1919. 
-Physiological Basis of Polarity. II. Journ. Gen. Physiol. 1, p.687.1919. 
(3) Priestley, J. H. The Mechanism of Root Pressure. New Phytol. 19 , 
pp. 189-200. 1920. 
