Physiological Studies in Plant Anatomy 265 
begins at the lenticel, before the phellogen forms a continuous layer 
encircling the cortex. Devaux’s extensive investigations provide 
other data of considerable interest, notably that the number of 
lenticels developed per internode suggest that lenticel formation is 
in direct relation to the vigour of growth of the shoot. As a result 
of his experimental analysis of the external and internal conditions 
leading to the formation of what he terms the primary lenticels 
upon a shoot, Devaux arrives at the conception that the formation 
of the lenticel depends upon an adequate supply of internal moisture, 
the “hydrose” of the tissue. As he also develops the idea that the 
continued functioning of the lenticel consists of an alternate closing, 
owing to extensive suberisation, and opening owing to the internal 
meristematic activity forcing the tissue through the hermetically 
sealed surface, an alternation of "cicatrisation" due to dryness of 
external and internal conditions and of proliferation due to excess 
of internal moisture, it is obvious that in one respect Devaux is very 
close to the point of view developed in this paper. 
He departs from it widely however in that he sees the cicatrisa¬ 
tion of the lenticel beginning with the proliferation of the sub- 
epidermal cells lining the stomatal chamber. He notes an early 
cutinisation of the surface of these cells lining the intercellular spaces 
bordering on the stoma (Devaux, loc. cit. pp. 81 and 97) but he 
regards this as a secondary feature. We should anticipate on the 
other hand that in this blocking of the surface cells bordering upon 
the stomatal chamber we have the causal feature preceding the sap 
accumulation, which in its turn brings about proliferation and the 
meristematic activity which results in the formation of the lenticel. 
Attention was therefore specially directed to this point, and upon 
examining sections of young intemodes of the stems of cork-forming 
plants clear evidence was obtained of the early cutinisation of the 
exposed surfaces of the cells bordering upon the stomatal chamber. 
In Pyrus torminalis Ehrb., Acer pseudoplatanus L. the first inter¬ 
node, in Sambucus nigra the second and in Syringa vulgaris L. the 
third, showed the clear red stain of a fatty deposit all round the 
surface of the stomatal cavity when sections were examined in 
Sudan III. 
It seems that when the endodermis is not functional the positive 
pressure of sap within the vascular strand will be effective in irri¬ 
gating the tissues right up to the subepidermal layer bordering upon 
the stoma which is probably thus supplied with water and solutes 
upon its free surface. As evaporation proceeds from this surface the 
Phyt. xxi. v. j8 
