54 
Proceedings of the Royal Society of Edinburgh. [Sess. 
been developed, two or more cells in isolated parts of the pericycle, in 
conjunction with several tracheids just below, were found to have enlarged 
Fig. 7. 
and extended outwards towards the endodermis. This enlarging of peri- 
cyclic cells appeared in a number of places, the endodermis becoming 
curved and broken as one cut 
further up from the root apex. 
The pressure of these thick- 
walled cells must have caused 
first that curving and then 
that splitting apart of the en- 
dodermal cells which is shown 
in fig. 8 and Photo I. The 
changes in the endodermal ring 
due to inside pressure occurred 
where there was greatest de- 
velopment of secondary tissue 
outside it, the cells of the 
secondary conjunctive tissue 
appearing to assist in the 
process of separation of its 
cells (see fig. 8, cells x v x 2 ). When the endodermis had been ruptured 
and the isolated parts pushed slightly outwards (fig. 9), the pericyclic 
