124 
Notes. 
the case at the later stages, for in the innermost layers of the 
exomeristem no more radial walls are formed, so that consequently 
the tangential diameter of these cells becomes very great. In the 
endomeristem, divisions having taken place freely towards the periphery, 
the junction of the tissues is made plain by the small-celled endo- 
meristem abutting directly on the large-celled exomeristem. For 
some time the layer of exomeristem immediately surrounding the 
endomeristem remains unchanged, but eventually each cell of this 
layer divides radially by a tangential wall, thus making the layer 
double; it is these two layers which eventually form the double 
endodermis so well known in Equisetum. Roots of E . hyemale , L. 
were used. The material was hardened with picric acid and de- 
hydrated with absolute alcohol; it was subsequently imbedded in 
hard parafin and sections cut with a microtome, the sections being 
carefully mounted in the order in which they were cut. 
J. REYNOLDS VAIZEY, Cambridge. 
POTTTS MONOPHYLLA (Torrey and Fremont).— This is a 
species which differs from its congeners by its ‘ solitary glaucous terete 
leaves’ (Sargent). Now, if the leaf were really solitary it would afford 
an illustration of a terminal leaf, the real existence of which has been 
denied. It must be remembered., however, that by some botanists 
the ‘ needles ’ of Pinus have been considered to be axial not foliar. 
Whether, however, there is any fundamental difference between axial 
and foliar structures is still to my mind a matter for doubt, but the 
point need not here be discussed, as for practical purposes, and es- 
pecially for the purposes of this communication, I assume that the 
two are really different. As, moreover, the axial nature of the typical 
Pine needle is now pretty generally discredited it is not necessary here 
to allude to the matter further, but as Bertrand 1 considers that the 
particular species now under discussion is exceptional, and that its 
4 needle ’ is really axial, it is advisable to cite what he says about it. 
‘ C’est une sorte de rameau dont le cylindre ligneux s’est ouvert 
suivant une de ses generatrices, et s’est etaie sur un plan tangent 
diametralement oppose a cette generatrice.’ Engelmann 2 says f it was 
1 Annales des Sciences Naturelles, ser. 5, Tom. xx (1874), p. 102. 
2 Botany of California, II. (1880), p. 124. 
