ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 759 
known, but in these the primary wood is of small extent and has much less prominent 
protoxylem angles (cf: Plate 20, photograph 14). Another distinction consists in the 
fact that the primary wood in the roots of Lyginodendron, when of comparable extent 
to that of the roots in question, contains a larger amount of conjunctive parenchyma. 
The difference in anatomical “habit” between the roots which we are describing 
and those of Lyginodendron is well marked, though easier to see than to describe 
(cf. photographs and figures of Lyginodendron roots with fig. 27 ). 
The cambium and phloém are exquisitely preserved in this and other specimens, 
The secondary thickening took place with remarkable regularity, the bands of 
secondary wood being strictly limited to the regions opposite the phloém. The 
pericycle appears to be several cells thick opposite the protoxylem. The inner 
cortex, which is a good deal crushed in most of the specimens, contained a large 
number of “ secretory sacs.” The large-celled outer cortex or “ epidermal layer ” is 
extremely conspicuous. 
Longitudinal sections of this form of root show little difference from the root of 
Lyginodendron, except the smaller amount of conjunctive tissue. 
From the evidence brought forward we feel no doubt, though the point is not yet 
strictly demonstrated, that the adventitious roots of Heterangium Grievit, like those 
of Lyginodendron, were of the Kaloxylon type of structure, but that the special form 
of root, characterized by a large tetrarch primary stele, with prominent protoxylem 
angles and little conjunctive tissue, was peculiar to Heterangiwm.* 
D. Hapit anp DIMENSIONS OF THE PLANT. 
As regards the dimensions of H. Grievii we have no evidence that the stem 
attained any larger size than is shown in our specimens, which reach a diameter of 
about 1°5 centim., though, of course, it is quite probable that it may have done so. 
The habit of the plant must have been like that of a small Lyginodendron. The 
stem was probably upright, as is indicated by its radial symmetry and strong 
mechanical construction. It bore spirally arranged, highly compound, Fern-like leaves, 
while in its lower part it gave off adventitious roots. The stem occasionally branched, 
though apparently this was rare. The general appearance of the plant would 
probably have been that of a Fern. 
As regards the fructification, we have no evidence which we regard as of any weight. 
We must, however, point out that the entire absence of any cone-like structure is 
remarkable, especially as in this case there is no reason to suppose that we have to 
do exclusively with young plants. This negative evidence, if we allow ourselves to 
be influenced by it at all, rather tends to favour the idea that the plant may have 
had a Fern-like form of fructification. 
* The best preparations showing this form of root are: C.N. 1885 H, 1915 B, D, M, O, P and R. 
The “quadrate Kalozylon” shown in C.N, 1635 is probably of the same nature. 
