165 
and Affinities of Nematophycus Logani. 
that the direction of all of them is not truly at right angles to the 
section. Thus, they are separated from each other by spaces often 
as great as the width of the opening, and sometimes much greater. 
The merest tyro in histological botany will see at once that we 
have gone sufficiently far in our investigation of this stem to show 
us that it cannot belong to a Phaenogamous plant. It wants the 
elements of the definite fibro-vascular bundles of the monocotyledon, 
and it wants also the elements of the indefinite fibro-vascular 
bundles of the angiospermous dicotyledon. Nor can it have any- 
thing whatever to do with the woody tissue of the gymnosperms, 
for the wood cells of the different bundles of these plants are 
universally and necessarily in close approximation, even in “ the 
young succulent twigs of some modern conifers,” in which Principal 
Dawson erroneously says the wood cells are loosely aggregated in 
relation to each other.* 
The space between the large openings is not uniformly 
structureless, but scattered throughout it can easily be detected 
openings of smaller size. The walls of these small openings are 
very delicate, and their interior is filled with mineral substance of 
the same colour and condition as that which invests them. In 
this respect they differ from the larger openings, which are filled 
with a less coloured and more transparent condition of the mineral. 
It is important to appreciate fully the mineral condition of this 
plant. It is entirely converted into amorphous silex, so that not 
only are the tissues replaced by this substance, but the spaces 
between the tissues and the cavities inside the tissues are completely 
filled with it. It is my purpose to deal one day with the different 
conditions under which fossil plants are preserved. It is too large 
a subject to treat of by the way. I would only say here that the 
condition of Nematopliycus is not uncommon, and that most beautiful 
specimens of the same condition occur in the silicified plants from 
Antigua. In the Brownian collection in the British Museum there 
is a specimen of the terminal bud of a palm, in which all the 
tissues are replaced with silica ; the interior of the cells and 
vessels are filled with this mineral, and the spaces between the 
leaves are occupied with the same substance which, from its colour 
and condition, was evidently supplied at the same time that the 
organized tissues were being fossilized. 
Occasionally spaces more or less free from organized tissues are 
seen passing through the structure in a somewhat radial direction 
(Plate XXXI., Fig. a). These are the medullary rays of Dr. Daw- 
son. It must, however, be noticed that the direction, though in a 
general way radial, is not strictly so, but that the spaces have an 
irregularly tortuous direction. Thus the sides of the spaces are very 
irregular, coming together here and there, swelling out into irregu- 
larly-shaped pouches, and turning off to the right or left. Further, 
* ‘Quart. Journ. Geol. Soc.,’ vol. xv., p. 484; ‘Pre-carb. Plants,’ p. 18. 
