Scott and Maslen . — The Structure of Trigonocarpus. 97 
In many Palaeozoic seeds with somewhat Cycadean organization, the 
micropylar region is elongated into a beak-like structure. Ordinary longi- 
tudinal sections of Trigonocarpus Parkinsoni commonly exhibit some trace 
of the micropylar beak, but it is rarely, if ever, preserved throughout its 
length. In many of the impressions, such as those from Newcastle figured 
in this paper (Pl. XII, Figs. 1 6, 17, and PL XIII, Fig. 18), the beak is about 
equal in length to the body of the seed, but as the sections show that the 
beak at the top was very slender and devoid of hard tissue, it is probable 
that part of it has been lost. In an impression of Trigonocarpus Parkinsoni 
figured in a paper by one of us 1 the long micropylar tube is quite double 
the length of the body of the seed, but this may possibly represent a distinct 
species from those described in this paper. In longitudinal sections of the 
petrified seeds, the micropylar beak is generally quite short, probably owing 
in some cases to the slightly oblique character of the section. In many 
cases it seems probable that the greater part of this elongated structure 
was broken off or had decayed prior to fossilization, when the seeds formed 
part of the medley of vegetable debris of which the coal-balls are 
composed. 
Taking the micropylar beak into account, the total length of a full- 
sized seed must have been at least 4-5 cm., and may have been greater 
than this. 
There is some evidence that the seed was attached to its parent axis 
by means of a stalk (see PI. XII, Fig. 12). 
A common feature of many of these old seeds is the possession of 
a thick two-layered testa, of which the outer thinner-walled zone or sarco - 
testa is always partly or entirely destroyed. The inner layer, which we 
shall describe as the sclerotesta ( = Williamson’s endotesta), consists of 
thick-walled elements, many cells in thickness, and all filled with dark 
contents. The sclerotesta bears three prominent ridges on its outer 
surface (PL XI, Fig. 5, /. /.), with corresponding furrows on the inner side 
marking the position of the three sutures, along which the testa may have 
split open when the seed was ripe. In each space between two main or 
principal ridges, are two, or more commonly three, less prominent eleva- 
tions which we shall describe as secondary ridges (PI. XI, Fig. 5, s. /.), 
so that the whole number of longitudinal ridges down the body of the seed 
is usually twelve. The ridges along the body of the seed undergo changes 
in number, and in the relative prominence of the principal and secondary 
ridges when traced upwards into the micropylar region, as will be described 
in detail later on in this paper. The degree of prominence of the various 
ridges is subject to considerable variation, even in the body of the seed ; in 
some specimens the secondary ridges are scarcely visible, and the sclerotesta 
consequently becomes only three-ridged. 
1 Scott (’05), (1) Fig. 33, p. 146. 
II 
