The Fossil Plants of the Coal Measures. 6 1 



Tracheids. 



F.— Fig. 3, A, B, C. C.N. 128, 



Cortex. 



p. 681, Fig. 5. See C.N. 149, 150, 151. 



p. 682, Fig. 11, C.N. 142. 



p. 681, Fig. 4, 5 (erroneously numbered Fig. 3 in the text). 



Terminal Twigs and Foliage of Petiole. 



F. — p. 683, Fig. 13.* See a similar example in C.N. 143. 



Structure of individual leaves. 

 See 193a and 1856. 



Double bundles escaping through the Cortex, to become vascular 

 bundles of leaf petioles (Rachiopteris aspera) of Lygi- 

 nodendron Oldhamium. 



R.— p. 89, Fig. 1, k. C.N. 1880. See also C.N. 1890 and 1150. 



C.N. 1980 (another section). 



C.N. 1981. A second section from the specimen 1980, but in which 

 the pair of bundles and their appropriate investments have 

 become almost completely detached from the parent Lyginoden- 

 dron, and become an ordinary example of the Rachiopteris 

 aspera. Thus, since the latter condition is a true fern frond, 

 we now know that at least one of the carboniferous ferns possessed 

 a true cambium by which was developed an elaborate zone of 

 exogenous secondary xylem possessing conspicuous medullary 

 rays. 



HETERANGIUM GRIEVII. Will. 

 This plant approximates so closely to Lyginodendron in 

 most features of its structure as to convince me that they 

 belong to the same division of the fern family. Their 

 distinctions are chiefly seen in the arrangements of the 

 tissues which occupy the interior of the medullary cavity. 

 Instead of finding the primary xylem, in its young state, 

 entirely filling that cavity, and ultimately breaking up into 

 about five very distinct masses, each of which adheres 

 closely to the inner margin of the secondary xylem, as is 

 the case with Lyginodendron, that central area of the stem 

 is partially filled with very numerous small bundles of 

 primary xylem, the intervals between which are firmly 

 occupied by a network of what apparently ought to have 

 been true medullary cells ; notwithstanding the peculiarity 

 of their position and arrangement, I venture, as I did in the 



*The original of this figure is in the Cabinet of my old friend, Mr. J. Butterworth, of 

 iShaw, near Oldham. 



