Note. 
533 
The petioles bear a considerable resemblance to those of the latter 
plant, from which they chiefly differ in the absence of cortical out- 
growths. 
C. The Root . 
1. Connexion between Root and Stem.— In several cases endogenous 
appendages, evidently adventitious roots, have been found arising 
from the stems of H. Grievii. In one specimen the bases of three 
such roots are seen in a vertical row, and the connexion of their 
tissues with those of the stem can be exactly traced. 
2. Structure of the Root.- — We have good evidence, though not so 
direct as in the case of Lyginodendron, that the roots of H. Grievii 
also belonged to the c Kaloxylon ’ type. A special form of root, with 
a large tetrarch stele of characteristic shape, seems to be peculiar to 
Heterangium. 
D. Habit and Dimensions of the Plant . 
In habit, Heterangium Grievii must have been similar to Lygino- 
dendron , but its dimensions were considerably smaller. Sporangia, 
like those of ferns, have occasionally been found in close association 
with the foliage, but not in connexion with it. 
ii. Heterangium tiliaeoides, Will. 
This species differs from H. Grievii in several points, but evidently 
belongs to the same genus. The specimens are from the coal- 
measures of Halifax l , and are remarkable for the astonishing per- 
fection with which the histological structure is preserved. The 
general anatomy was fully described in 1887. In primary structure 
the stele agrees with that of H. Grievii, but the peripheral bundles 
are more distinct. The secondary tissues are subdivided by broad 
primary rays (enormously dilated in the phloem), which correspond 
to the conjunctive tissue separating the primary bundles. Cambium 
and phloem are perfectly preserved ; the latter is of great thickness, 
almost equal to that of the secondary wood. So perfect is the preser- 
vation, that stages in the development of the tracheides from the 
cambium have been observed, while the compound sieve-plates on 
the radial walls of the sieve-tubes are quite clear. Sclerotic groups 
1 Williamson, Organization, Part XIII, 1887. 
