188 TRANSACTIONS OF THE [Sess. lixxvi 



Las yet to be worked out before the topic can be in any sense 

 of the word completed. 



Finally, I wish to thank Professor W. Wright Smith, Regius 

 Keeper of the Royal Botanic Garden, Edinburgh, for providing 

 facilities for carrying out the investigation. 



References. 



(1) Crevost, (h., and De Fenis, F. : Bull. Ec. de L'Indochine, xxiv, 



1921. 



(2) Solereder, H. : Systematic Anatomy of Dicotyledons, 1908. 



(3) SoRAUER, P. : Physiology of Plants, Trans. Weiss., 1895. 



(4) Stoll, R. : Uber die Bildung des Kallus bei Stecklingen, Bot. Zeit., 



xxii, 1874. 



(5) Simon, S. : Experimentelle Untersuchungen Uber die Differenzier- 



ungsvorgange in Callusgewebe von Holzgewachsen, Jahr. wiss. 

 Bot., xlv, 1908. 



EXPLANATION OF PLATES IX.-XI. 



Fig. 1. Cuttings nine weeks old, made at 10-12 internodes. Heavy 

 callus formation is visible on the etiolated shoot on the left, 

 while the normal shoot on the right has no callus visible, 

 xi 



Fig. 2. Cuttings ten days old of normal shoots which are etiolated 

 under an inverted flower-pot, forming callus at the apex 

 about the 4th internode, X ^. 



Fig. 3. Transverse section of normal stem, 7th-8th internode, with 

 crescents of j^ericyclic stereom opposite the phloem joined 

 by stone cells. The lignified cells show protoplasmic 

 contents, X 175. 



Fig. 4. Transverse section of etiolated stem, 7th-8th internode, 

 showing the now thin-walled cells of the pericycle with large 

 ])rotoj)lasaiic contents in striking contrast with the char- 

 acter before etiolation in fig. 3, X 175. 



Fig. 5. Lcmgitudinal section of etiolated cutting five weeks old, 

 showing formation of callus by meristematic activity of 

 cambium, X 68. 



Fig. 6. Longitudinal section of etiolated cutting five days old, with 

 the pith cells in active division, the new cell walls being 

 laid down at right angles to the cut surface, x 175. 



