540 Du tt.—Pityostrobus macrocephalus , L . and H. 
sort of internal structure as those of P. macrocephalus. The nucellus 
partly lines the integument and is partly free from it. It is always in 
connexion with the integument at the shoulders of the ovule, and there 
are nearly always indications of a well-developed apical column. Fig. io, 
PL XV, which represents the upper part of a large ovule cut obliquely 
longitudinally, gives some idea of the stage of development shown in 
these sections. In this, as in many other examples, the structural 
features of the micellar tissue are well preserved. They can easily be 
made out in the patch of tissue on the right-hand side of the photograph, 
especially when examined with a lens. The tissue is rarely more than 
one cell layer in thickness, and the thin walls of the separate cells have 
often been finely preserved. The cells are comparatively uniform in size, 
the whole structure forming a network of narrow elongated meshes. The 
characters just mentioned afford a criterion by means of which it is possible 
to recognize the nucellus in several cases which would otherwise be 
doubtful. Thus it often happens that by this means it is possible to 
distinguish both nucellar and integumentary tissue in a layer in which 
the double morphological origin is not immediately obvious. It, of course, 
affords decisive evidence of the nucellar nature of the tissue surrounding 
the prothallus in the ovule of Fig. 9, PI. XV. 
(iii) The Nucellar Column. 
More or less definite evidence of the existence of this peculiar feature 
is to be found in almost every longitudinal section of an ovule. It is 
evident from the photographs (Figs. 7, 10, 11, 13) that this structure 
does not form a nucellar beak, but is rather a cylindrical column of 
parenchymatous or somewhat thick-walled cells which may exhibit the 
typical structure of the nucellar tissue as seen elsewhere. This paren- 
chymatous structure is especially distinct at the base of the column 
where there is a shallow, moat-like depression (see Fig. 13, PI. XV). 
In the ovules of the Sedgwick Museum cone the structure of the 
nucellar apex is exhibited with exceptional clearness. The typical 
columnar form is usually represented, but the darker opaque portion ap- 
pears irregularly broken into bands separated by clearer spaces, and is very 
suggestive of permeation by a number of pollen-tubes (see Fig. 1 5, 
PI. XV). The cellular framework is also coarser than usual— -the cells 
being elongated and the walls thicker and darker, though the charac- 
teristic fine meshwork tissue is often evident in the lower part of the 
column. There is one case in which only the thick outer wall of the column 
has been preserved, and this is not continuous across the apex, so that here 
the beak actually appears as a hollow open chamber with contorted sides. 
In the thicker sections from the other cones where the whole of the beak 
is seen it almost invariably is dark-coloured and opaque or encloses an opaque 
