24 Tansley and Chick —Notes on the 
to the appearance as we pass upwards of the two mantles of 
the stele. Thus we pass to the typical structure of the leafy 
aerial stem. 
Aerial leafy Stem. 
The histology of this has been described by Haberlandt 
and Bastit in P. juniperinum, and by Coesfeld in P . commune. 
To the former we owe the first good detailed account of its 
structure. Haberlandt finds the peripheral hydrom-mantle 
surrounded by a layer of leptom three or four cells thick, 
composed of (a) wider sieve-tube-like cells, and (b) narrower 
cells with oblique end-walls corresponding with ‘ cambiform ’ 
(elongated phloem-parenchyma) in Angiosperms. The only 
other differentiation in the leptom is the suberization of the 
walls of the inner layer or two of cells. These suberized 
cells do not, however, according to Haberlandt, differ in form 
or contents from the outer unsuberized layers (cf. his Fig. it, 
Taf. XXIII). We find, on the contrary, in agreement with 
Strasburger 1 , Goebel 2 , and Coesfeld 3 , that the peripheral 
hydrom-mantle is immediately surrounded by one or two 
layers of cells with dark brown suberized walls and starchy con- 
tents, in fact an amylom-layer — the walls of which, according 
to Coesfeld (op. cit.), are folded like those of an endodermis — 
our hydrom-sheath , while immediately outside this comes 
a layer interrupted here and there by starchy cells, and rarely 
more than one cell thick, of typical sieve-tube-like cells or 
leptoids with no starch and light walls — the leptom-mantle. 
This is strangely neglected by the recent writers on the 
subject, Coesfeld (op. cit.) and Strasburger (Bot. Practicum, 
2nd ed., 1897), although it is extremely easy to distinguish 
in P. comimtne on staining with iodine. External to the 
leptom-mantle comes a layer of cells shading into the inner 
cortex, but of rather less diameter, with rather thinner, nearly 
colourless walls, and particularly abundant starchy contents. 
1 Botanisches Practicum, 1st ed., 1884, P* 304. 
2 Muscineen, in Schenk’s Handbuch, ii, p. 369. 
3 Beitrage zur Anat. u. Phys. der Laubmoose, Bot. Zeit., 1892, 
