202 Prof. W. 0. Williamson and Dr. D. H. Scott. [June 13, 



petiole of H. Grievii usually receives from the stem a single bundle 

 only. 



2. Form and Structure of the Leaf. We find innumerable portions 

 of petioles, varying from 4 mm. to 0'4 mm. in diameter, sometimes 

 branching, and intermixed with fragments of leaflets. We can only 

 infer that the leaf of H. Grievii was a highly compound one, probably 

 not very different from that of Lyginodendron. 



The petiole is traversed by a single bundle of concentric structure. 

 Thus the bundles underwent the same change on entering the leaf as 

 in Lyginodendron. 



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 " 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, Heterancjium 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 tiliceoides, 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,* 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 



* Williamson, " Organisation," Part XIII, 1887. 



