12 Oliver and Salisbury. — On the S true here and 
most nearly vertical being R. hi, PI. I, Fig. i. The others fall into two 
categories with regard to their direction, viz. : — 
1. Sections in which the plane of symmetry passes through a rib 
or angle (e. g. R. no, PI. I, Fig. 10) will taper above and below — the two 
ends appearing longer and more pointed as the plane of section approaches 
the vertical, shorter and more rounded as it approaches the transverse. 
2. Those in which the plane of symmetry falls between two ribs, the 
sections appearing boat to coffin shaped according as they pass through 
the apex or not. 
Asymmetrical variations of these two types are the rule, due to the 
median plane of the section falling between the planes of symmetry (the 
median plane being that radial plane of the seed which is cut at right 
angles), or more strictly — regarded as variations of these two groups — due 
to obliquity of the plane of section to one of these planes of symmetry. 
Section R. 119, 1 (PL I, Fig. 11) is a good example of such a variation 
of the second type. The outline is roughly that of a coffin with sloping 
ends, the upper half foreshortened owing to the tapering of the apex ; as will 
be seen from the plotting on the transverse diagram (Text-fig. 2) the plane 
of section stands asymmetrically with regard to the two ribs first cut 
(r 1 and r 2 ). For convenience of description, such sections may be termed 
doubly oblique. In the case of a perfectly cylindrical seed doubly oblique 
sections are not possible, since the plane of any section is always at right 
angles to a plane of symmetry. In a ribbed seed, the number of planes of 
symmetry being only twice that of the ribs, where these, as in the present 
instance, are few, it is only rarely that a section presents a regular outline. 
It appears highly probable that sclerization of the hard testa took 
place in an acropetal direction. This is suggested by two of the seeds which 
on general grounds we regard as immature. In the first of these (R. 122, 
PI. I, Fig. 3) the soft- celled tissue ( s.t .) which constituted the apical cap 
is not sharply delimited from the hard tissue below (/.), as is the case 
in the mature condition, where the demarcation was sufficiently abrupt 
to have fissured, in some cases, along this line (W. 267, PL I, Fig. 8, s.t.). 
This seed (R. 122) would furthermore appear to be young, since the 4 blow- 
off’ layer is mostly in situ , and also the plinth, which having regard to the 
plane of section should have been cut across, is not present — a fact which 
seems to indicate the later development of this structure. 
The second example of a young seed (R. 114) also shows less scleriza- 
tion of the testa cells — their contents, usually so obscure, being here 
comparatively well defined (PL I, Fig. 2). The presence of the pad of 
tissue beneath the lagenostome with well-preserved cells (Is.), the exhibition 
of cellular structure by the integumental lining, and a plinth only half the 
height of those in the mature seeds, all seem to point in the same direction. 
