442 
SPENCER : ASTROMYELON. 
the pith is absent. There is such a striking- difference between 
the two extreme forms, that were it not that a large series of 
specimens shew a complete gradation between them, they might 
be considered as separate species ; some specimens have the 
woody wedges clearly formed but the pith has disappeared ; other 
specimens shew a continuous cylinder without even a trace of 
wedges and a hollow space in the centre. 
In my paper on " Astromyelon and its Root," Avhich I read 
before the Geological Section of the British Association at York, 
I described two new forms of Amyeloid Roots, which I believe 
are the roots of Astromyelon. It must be premised however that 
they have not been discovered connected with the plant. 
The new specimens in my collection belong to the class of 
pithless roots which Professor Williamson has described under the 
name of " Amyelon." 
One of these Amyelon radiccms is regarded as one of the roots 
of Asterophyllites ; it bears the closest resemblance to the new 
specimens and it may be advisable to give a short description of 
it. Amyelon radicans has a solid vascular axis, formed of com- 
paritively large vessels, which are plain on their tangential faces 
and reticulated on their radial faces ; the bark is rarely preserved, 
but when a portion is met with it is seen to be of rather loose 
texture. The most characteristic feature of this plant is the 
beautiful reticulations on the cells. The cells in the stem of 
Asterophyllites are also beautifully reticulated, and it was from 
the peculiar character of these reticulations and their being con- 
fined to the radial faces of the vessels, that is to the sides of 
the vessels facing the medullary rays in each plant, that their affi- 
nities were established. 
I have already pointed out that under the name of Astrome- 
lon a very widely divergent group of plants are comprehended, 
which may be necessary to be divided into two or more species. 
The common form with the star-like pith forms one group, while 
those with little or no pith may form another. The root which I 
