Scott and Mas leu . — The St nature of Trigonocarpus . 107 
In many transverse sections one or more of the principal ridges shows 
a central crack as though the seed naturally split open along these sutures 
(see PL XI, Figs. 5, 6). This splitting is never seen in relation to the 
secondary ribs. 
The principal ridges when traced from the centre of the body of 
the seed upwards to and along the micropylar beak gradually become less 
prominent and ultimately disappear. This change will be seen by ex- 
amining the series of transverse sections represented in PL XI, Figs. 5-8. 
Fig. 5 is cut near the centre of the body of the seed and exhibits 
what may be called the normal arrangement, the principal ridges being 
easily distinguished by their size. In Fig. 6, which is cut at a some- 
what higher level than Fig. 5, these ridges are still sufficiently large to 
be readily identified even without the characteristic splitting which is 
well shown in this slide. In Pig. 7, which is cut across the lower part 
of the micropylar beak the principal ridges of the body of the seed appear 
opposite to the angles of the triangular micropylar tube and although 
still large, some of the secondary ridges have become equal to them. Lastly, 
in Fig. 8, which is cut higher up the micropylar beak, the principal ridges 
lying opposite to the points of the micropylar canal have practically 
disappeared altogether. 
Passing to the secondary ridges, these are also found to vary con- 
siderably in different specimens and at different levels. In a typical 
example, a section across the central part of the body of the seed, such 
as PL XI, Fig. 5, shows the three secondary ridges, t., lying between two 
principal ribs and about equally developed. In some cases, however, 
the median ridge of each set of three is so slightly developed as to be 
practically absent, so reducing the total number of ridges (principal and 
secondary) to nine, while in yet other examples all the secondary ridges 
are ill-developed so that only the three principal ridges are at all con- 
spicuous. Changes also take place in the secondary ridges when they 
are traced upwards as will be seen by again examining the series of 
transverse sections at various levels (PL XI, Figs. 5-8). In Fig. 5 all the 
secondary ridges are about equally developed ; in Fig. 6 which is cut 
at a higher level the central ridge of each set of three has ‘flattened out’ 
so that it has nearly disappeared while the two lateral secondary ridges are 
equally prominent ; in the still higher sections while the lateral secondary 
ridges still remain conspicuous the central one is unrepresented. Hence 
the most persistent longitudinal ridges appear to be the lateral secondary 
ribs, or those to which the sarcotestal bundles are probably opposite, as we 
have previously shown. 
A knowledge of these regional variations in the ridges of the sclero- 
testa is of some importance in the attempt to interpret the structures seen in 
casts, as will be explained later. 
