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Proceedings of the Royal Society of Edinburgh. [Sess. 
behaviour of endodermis in the secondarily thickened roots of other species 
of Dracaena, and the phenomenon of the penetration of parenchyma cells 
between thicker-walled cells, with the consequent splitting apart of the 
latter, has been shown by others to occur elsewhere. Schwendener (2) 
figured a cross-section of a root of Convallaria majalis showing the 
interruption of the endodermis by thin- walled parenchyma ; and Miss A. M. 
Clark (6) has described an ingrowing of parenchyma among secondary 
xylem elements in the stem of Kendriclcia Wallceri. In fig. 11 I have 
demonstrated an example of the intrusion of parenchyma from the cortex 
which seems to correspond in its nature and origin to the case of 
Convallaria mentioned by Schwendener. This intrusion into the endo- 
dermis occurred before the appearance of cambium at that point, though 
secondary thickening was active at the opposite side of the root. 
In conclusion, I wish to acknowledge my indebtedness and grateful 
thanks to Professor Bower for so kindly supervising the work, and to 
Dr J. M. Thompson for valuable criticism. 
REFERENCES. 
(1) Haberlandt, G., Physiological Plant Anatomy, 1914, Oxford translation. 
(2) Schwendener, S., Die Schutzscheiden und ihre Verstdrkungen , 1882. 
(3) Bower, F. O., Professor, Presidential Address to Royal Society of 
Edinburgh, 1920, Proc., vol. xli, p. 1. 
(4) Spratt, A. V., Miss, “ Some Anomalies in Monocotyledon Roots,” Annals of 
Botany, 1920. 
(5) Scott and Brebner, “The Secondary Tissues in certain Monocotyledons,” 
Annals of Botany, 1893. 
(6) Clark, A. M., Miss, “ Secondary Thickening in Kendrickia Walkeri,” Annals 
of Botany, 1907. 
ILLUSTRATIONS. 
E. = endodermis : p. = pericycle : c. = cambium : phi. = phloem: xy. = xylem: 
Pr. tis. = primary tissue : Sec. tis. = secondary tissue : cor. = cortex. 
Text-Figures. 
Fig. 1. Endodermis complete without cambium on either side. x 250. 
Fig. 2. Endodermis complete with pericyclic cambium. x 250. 
Fig. 3. Separation of endodermal cells by internal cambial activity. Inter- 
cellular spaces are numerous in the thin-walled tissue. x 250. 
Figs. 4 and 5. Steps in the breaking up and displacement of endodermis by 
intrusion of parenchyma cells. x 250. 
