OF THE FOSSIL PLANTS OF THE COAL-MEASTJBES. 
251 
hence the triangular aperture (d) of the previous figure now exhibits oblate sides. In 
fig. 102 this enlargement of the nucular cavity becomes yet more conspicuous, and in 
fig. 103 a further expansion of that cavity has taken place, whilst in its interior we 
now find the upper part of the nucular membrane f Unfortunately the section has 
just missed the lagenostome (c) of figs. 96, 97, and 98. In fig. 104 the nucular 
membrane (f) is further enlarged, and within it is the perispermic membrane (y). 
Similar arrangements continue to appear in the sections (figs. 105 & 106), save that in 
them the perispermic membrane (y) has collapsed to one side of the nucular membrane 
(f), and the latter is beginning to show a ragged outline on its external surface. In 
fig. 107 we have passed below the greatest diameter of the seed. The exterior of the 
nucular membrane is becoming yet more ragged, indicative of its forcible detachment 
from the inner surface of the endotesta; whilst in fig. 108 we have reached the base 
of the perispermic membrane (y) and approached the chalaza. Parts of two sections 
successively made yet lower down are represented in figs. 109 and 110, the former in the 
endotesta and the latter in the sarcotesta. To these further reference will be made. 
The letters of reference appended to the various ridges of the endotesta in fig. 100 
are similarly attached to the same parts in fig. 103, in which these ridges are very 
clearly exhibited. Fig. 104 shows with perfect clearness that an inorganic cast of the 
interior of the cavity of the endotesta made after the nucleus and its two investing 
membranes had disappeared would exactly correspond with what we see in fig. 94. 
It is sufficiently easy to discern the real nature of “ the three conspicuous salient 
ridges ” spoken of by Professor Newberry. They were portions of the inorganic cast 
filling the three very narrow slits within the three chief prominent ridges of the endw 
testa ( b', b', b'). The several sections (figs. 101, 104, 105, 107, & 108) show that the 
three radiating slits in the endotesta are the largest and deepest at the upper parts of 
the seed, and that they diminish in size as we approach the centre of the seed, below 
which they grow rapidly less as we approach the chalaza, when they almost disappear — 
conditions that are identical with what we find in fig. 94. The exterior of the seed 
exhibits nothing to correspond either with the three thin “broad and delicate wings,” 
or with the smooth convex surface of the “ nut ” in fig. 94 ; but the internal cavity of 
the endotesta displays all these characteristics with the most minute exactness. I think 
that doubts as to the correctness of my explanation of the common sandstone specimens 
of Trigonocarpon olivceforme and its numerous near congeners can no longer be enter- 
tained. 
The minute structures of the various investments of this seed have already been 
described by Dr. Hooker and Mr. Binney ; but it is obvious that they are subject to 
some variation. Fig. Ill exhibits a portion of a vertical section through the testa, and 
fig. 112 a similar transverse section through the same tissues; both of them enlarged 
62 diameters. 
In fig. Ill we see that the sarcotesta (a) consists of a parenchyma with very thin 
cell-walls, and with the cells approximately uniform in size. The endotesta (b), on the 
