792 
Notes. 
THE ‘ EPIDERMOID AL * LAYER OF CALAMITE ROOTS — 
The bounding layer of young calamite roots consists of cells with 
thick outer membranes. These are in no way specially remarkable, 
being cells which have ‘ the structure of a thick-walled epidermis, and 
appear to correspond in all respects with the epidermoidal layer 
described by Olivier in many recent roots' 3 . As is seen from the 
published figures 1 2 they are much the same size as the cells of the 
cortex (diameter about *o8 mm.), and do not stand out from them in 
any very remarkable way, except in the thickness of the external wall. 
In foreign specimens of older roots a periderm of nine to twelve 
layers has been described by M. Renault 3 , but the outermost layer 
does not appear to have differed from the ones below it. No such 
definite periderm has been described for English roots. In the above 
1 Williamson and Scott, Further Observations, II, Phil. Trans., 1895, p. 694. 
2 loc. cit., PI. XV, Phot. 5, PI. XVII, Figs. 7 and 8. 
3 Genre Astromyelon, Ann. des Sci. Geol., 1885, vol. xvii, Fig. 2, PI. VII. 
