538 Dutt , — Pityostrobus macrocephalus , L, and H. 
three specimens. There is an outer layer which has usually been completely 
carbonized, though in some places the crushed remains of thin-walled cells 
adhere to the inner layers. From the manner of preservation it is clear that 
this represents the remains of an outer fleshy layer. Next comes a wide 
zone of well-preserved, thick-walled cells, obviously representing a ‘ stony 
layer s . As the photographs show, the outline of this towards the exterior 
is very irregular, indicating that the surface must have been marked by 
projecting ridges, which in some places are very prominent. The testa of 
the ovule of Pinostrobus sussexiensis , already referred to, appears to have 
possessed much the same structure. In reference to this Dr. Stopes remarks, 
* In section, the stony layer of the testa is much indented and is irregularly 
star-shaped in outline, which appears to represent surface-corrugations. 
How far these are natural, and how far petrifact, the sections do not afford 
data to determine’ ( 13 , p. 127). In the less well preserved tissue of the 
integument of P. ovatus the interior of this stony layer has often been partly 
decomposed, leaving spaces filled with black, carbonaceous granules. This 
is especially common in the interior of the larger ridges. 
Towards the inside the stony layer merges gradually into a less heavily 
sclerized zone, the cells of which are rendered conspicuous by their polygonal 
outlines and distinct lumen. These cells are more or less isodiametric, while 
those external to them are usually somewhat radially elongated. On the 
inside again there is a transition to small thick-walled cells, but their 
structure is not easily discernible and they appear to pass insensibly into 
the layer of crushed, fibrous-like cells which form the inner lining of the 
integument, and which has often become separated from the main part of 
the wall. This is very noticeable in the ovule seen in Fig. 9, PI. XV, where 
the inner layer is only in connexion with the ovule at the very base. 
(ii) The Nucellus. 
Except in the apical region, only a thin layer of this tissue has been 
preserved. In the ovule mentioned above (Fig. 9, PL XV) it might appear 
at first sight as if the nucellus were free from the integument from the base 
upwards, but on a little closer examination it becomes evident that the 
nucellus is coalescent with the separated wall of the integument and only 
becomes free in the upper portion. In this ovule, moreover, the relations 
of the different structures are rendered perfectly clear by reason of the 
separate, distinct outline of the small crumpled prothallus which occupies 
the centre. Many of the other sections, however, are more difficult to 
interpret. A good example is the well-preserved ovule of Fig. 1, PI. XV. 
In this ovule it would seem as if the cavity were nearly filled by a well- 
rounded prothallus which exhibits an extraordinary beak-like prolongation 
in its apical region. The rather shadowy surrounding tissue appears to be 
lifted up by the beak, so that the whole structure at once calls to mind the 
