The Carboniferous Arborescent Lepidodendra. 49 



has doubtless arisen from the small number of specimens 

 that we have hitherto obtained of this rare type. On the 

 other hand, unequal dichotomies are frequent. Thus, in the 

 two fine young sections of the same branch, 380a and 390b, 

 lateral branches are being given off from opposite sides of the 

 central branch ; but in both cases the secondary branches 

 of the primary xylem are of the solid type, invariably found 

 when such bundles are destined to supply Halonidal 

 tubercles and similar fruit-bearing organs. In N. 1596a, 

 section B, we discover the origin of such bundles, as repre- 

 sented in Memoir XIX., Fig. 1, where we have the segment 

 b' becoming detached from the Primary Xylem cylinder b. 

 We also have an excellent illustration of the course of a 

 similar bundle going to the abortive branch B, in Fig. 29 of 

 the same Memoir. {See C.N. 1596D.) 



Type of Lepidodendron fuliginosum. 



Very young examples of this type are more rare than 

 those of more advanced growth, but this may be partly due 

 to the fact that such examples are not easily identified as 

 belonging to the type. It is only in such as are of more 

 advanced growth that the characteristic features of the 

 type assume their distinctive aspects ; but we certainly have 

 such an example in C.N. 379*. (Table V.) A segment has 

 been separated from the cylinder of Primary Xylem, which 

 cylinder has a diameter of about 3 '5 mm. Measuring the 

 defective portion of the cylinder I calculate that its 

 tracheids have not exceeded 800. Its medulla had a 

 diameter of 2 mm. In 379 — the branch was a larger 

 one. Its primary cylinder had a diameter of 4/5. I was 

 unable to estimate its component tracheids, but its medulla 

 had enlarged to 2*5, all which enlarged features suggest a 

 further increase in the number of the primary tracheids. 

 In C.N. 1 922 A, the diameter of the primary cylinder is 



