io6 Scott and Mas leu. —The Structure of T rigo nocarpus, 
preservation the evidence is not conclusive. More perfectly preserved 
sarcotestal bundles at the base of the seed afford evidence of a more 
complex structure which may be compared with that of Cycas Beddomii , 
as will be explained in detail in our description of the lower end of the 
seed (p. 115). 
The Sclerotesta. We may now consider some of the details of the hard 
layer of the testa, the sclerotesta, which lies within the sclerotesta. The 
structure of the sclerotesta has been previously described in some detail by 
Hooker and Binney \ and later by Williamson 2 , and as far as internal 
structure is concerned we have but little to add to their descriptions. This 
hard layer forms a complete investment to the seed excepting only at 
the upper end of the long micropylar beak, where it is, of course, perforated 
by the opening of the micropylar canal. Its thickness, when measured 
between the ridges of the body of the seed, in such a section as that shown 
in PI. XI, Fig. 5, j. t. y is 1-1*5 mm * Most longitudinal sections show a 
thickening of the sclerotesta as it is traced from the chalaza upwards 
to the base of the micropylar beak. This may also be seen in some of 
the transverse sections, as by comparing PI. XI, Pig. 5, and PI. XI, Fig. 7, 
the former cut across the central part of the body of the seed, and the 
latter across the lower part of the micropylar beak, although as the 
two sections are not cut from the same seed the comparison as to thickness 
must not be carried too far. Comparison may also be made of PI. XII, 
Fig. 12 and Fig. 13, which are longitudinal sections of the lower part, and 
of the upper part respectively, of two seeds; in Fig. 12 the thickness 
of the sclerotesta is at its thinnest part about *8 mm., while in Fig. 13 
the maximum thickness is 2 mm. The sclerotesta of the lower part 
of the same seed as that figured in PI. XII, Fig. 13, has a thickness of 
only 1 mm. 
As already briefly described the sclerotesta has a very characteristic 
form when seen in transverse sections. The normal number of ribs pro- 
jecting on the outer side is . probably always twelve in sections cut across 
the body of the seed, such as PI. XI, Fig. 5. The twelve ribs are usually 
easily distinguishable into two sets, the principal ribs (PI. XI, Fig. 5, /. t'.) 
always three in number, and the smaller or secondary ridges (PI. XI, 
Fig. 5, s. t.) usually nine in number. The degree of prominence of the principal 
ridges is subject to considerable variation in different seeds as well as at 
different levels of the same seed. In most specimens the principal ridges 
are readily distinguished from the secondary ones by their greater promin- 
ence as shown in PL XI, Figs. 5, 6. In some other seeds the principal 
ridges are broader and less pointed, and in yet other cases there is only 
a slight difference in size and shape between these and the secondary 
ridges. 
1 Hooker and Binney (’55). 
3 Williamson (’77), p. 252 , 
