The Carboniferous Arborescent Lepidodendra. 51 



branch, perforated by ten well-defined leaf-traces. This 

 section alone threw no light upon the future history of the 

 detached branch. But fortunately another specimen, C.N. 

 1654, supplies the information needed, in a series of 

 eleven sections (C.N. 1654 to 1664) made at various 

 transverse levels of the same branch. In Memoir XVI., 

 Fig. 1, the segment b' is shown becoming detached from 

 the primary cylinder b. In Fig. 3 we have the separated 

 segment, carrying along with it a little of the central 

 medulla of the primary cylinder, whilst at Fig. 2, b, b, we 

 have the condition of the gap in that cylinder left by the 

 detachment of Fig. 2. The more important changes under- 

 gone by the segment are seen in Figs. 4, 5, and 6, the last 

 of which exhibits an oval bundle, composed wholly of 140 

 large and small tracheids ; a fac-simile of all others 

 originated by the same process of segmentation. 



The above examples correspond in their teachings with 

 the types previously described. C.N. 1653 demonstrates 

 that their ordinary equal dichotomies are identical with 

 the rest of the Lepidodendroid family, and the same obser- 

 vation applies to the unequal dichotomies. One more 

 condition requiring attention exists in this fuliginosum type. 

 I was long unable to discover any secondary xylem in their 

 branches. At length, however, I obtained the section C.N. 

 387 (See Memoir XI. Fig. 11, hh') and other similar 

 examples, C.N. 1592 bis and 1592 A, have since come into 

 my possession. The cells of the innermost cortex of this 

 type are arranged in radial lines, and amongst these lines 

 we find parallel ones of true tracheids, rudimentary repre- 

 sentatives of the secondary xylem zone. In the longitu- 

 dinal section these tracheids pursue a very irregular, undu- 

 lating course, and they are very unequally distributed in the 

 cortical ring in which they occur. I have seen no trace of 

 this Secondary Xylem in young branches. As usual, it 

 obviously indicates a more advanced stage of growth. 



