Apr. 1904.] BOTANICAL SOCIETY OF EDINBURGH 453 



affects the argument, as once division has been set up, 

 and the meristematic condition definitely assumed, the 

 lenticellar elements, from being merely passive structures 

 acted on by pressures induced by a relatively distant 

 cambium, enter an active condition, and in their turn 

 exert positive pressures on the inactive tissues in their 

 neighbourhood. In the case of stems with deep periderms 

 the relation between the structures is more complicated, 

 but even here, according to Devaux, the Lenticels arise 

 beneath subtending stomata. The intervening tissue, 

 though possibly rendering the release of pressure due to 

 the stoma more diffuse, can hardly exert any marked 

 pressure on its own account, so that in this case also the 

 active stresses are those due to the epidermis. 



The origin of Lenticels on leaf scars, as in Ahies pcctinaia. 

 Daphne, etc., though still requiring further elucidation, also 

 seems to point in the direction of initiation under conditions 

 of minimal pressure. In these cases the Lenticels apparently 

 arise before the fall of the leaf, in the phylloptotic phellogen, 

 and are therefore in a position in which radial pressure is 

 greatly reduced owing to the absence of an elastic epidermis, 

 while the base of the leaf, largely composed of dead parenchyma, 

 can scarcely exert any great force on the surface of the 

 abscission layer. 



Those Lenticels which occur in pairs, one on each side 

 of a leaf scar but apparently external to it, still require 

 more accurate investigation, with the object of determining 

 their point of origin ; as it may possibly happen than they 

 will ultimately fall to be included in the same category as 

 those of Abies and Daphne. 



As regards the Lenticels described by Weiss in stems 

 of monocotyledons where they bear a definite relation to 

 the axillary buds, further information is also still required. 



We have now to consider the conditions under which 

 Lenticels arise in roots. As Devaux points out, these are 

 always situated at the bases of lateral rootlets lying either 

 to right and left or directly above and below them. 



The accompanying figures, however, show that this is 

 but a partial statement of the case, so far at least as 

 concerns the point of origin. 



The primary Lenticels of a root normally arise beneath 



