380 PROF. F. W. OLIVER ON THE STRUCTURE 
(a) Complete Pollen-grains.—The external features are shown by the grain p.? (text- 
fig. 2, and Pl. 44. fig. 42). It is oval and evidently flattened in the plane of the section. 
Its dimensions are 914 72 u. Its area is divided into a peripheral gently convex region 
anda central strongly convex boss. Both the wing-like periphery and the central boss are 
sculptured. The former is marked with radially running lines, the latter with a reticu- 
lated sculpturing (fig. 42, p.?). The grain is marked with a triradiate slit (fig. 42, £7.s.) 
on the convex central region, possibly an indication of its origin as a member of a tetrad. 
Median longitudinal section of Stephanospermum caryoides. 
Outside is the integument or sclerotesta (st.), with its epithelioid lining (et.); within it, fragments of the endotesta 
(end.t.) are represented ; m., micropyle. The broad nucellus contains the pollen-chamber (p.c.) above, 
a marking its apex; sh., peripheral tissue (shoulder) of pollen-chamber with well-marked epidermis ; 
P+» p^, &c, the various pollen-grains referred to in the text; x X, position of possible antherozoids ; 
8.a.g., Supra-archegonial gap; ¢.m., the tracheal mantle, ending at b; t.d., tracheal dise ; m.w., wall of macro- 
spore. x 61. 
This pollen-grain is rather opaque, but details of the internal structure are provided by 
P: represented in fig. 40 (dimensions of p.,110 LX 15 u). In this grain parts of the 
boss — been ground away in the preparation of the section. Focussing through the 
boss two internal cells are distinctly seen (a & 5, Pl. 44, fig. 40), a smaller cell and a larger 
Seg pe surrounding it. The contents of the larger cell (a) seem to be preserved. The 
irregular space c, at the right-hand bottom corner of the grain, appears to bean extension 
of the outer cavity of the pollen-grain—to be a pollen-tube, in fact. Two alternatives to 
