202 
PROFESSOR W. C. WILLIAMSOR OR THE ORGARISATIOR 
continued to grow after the strobili had dropped off.'" The illustration given above 
also tends to confirm statements made in my Memoir, Part X. (‘Phil. Trans.,’ 1880, 
p. 493), when describing the Arran Lepidodendron. I there gave my reasons for 
believing that, though no medulla was present in the centre of the vascular axis of 
any of the young twigs and branches of that branch, one had somehow or other been 
developed at a later stage of growth in those vascular bundles. Other conditions of 
these Arran specimens being considered, it now becomes an almost absolute certainty 
that such had been the case. The history of figs. 19, 20, and 21 of the present Memoir 
bears upon the same question, but little more can be said in reference to this latter 
plant until we obtain specimens of it in a more advanced state of growth. Though it 
and the Arran plant possess several features in common, I cannot identify them with 
sufficient definiteness to assign the same name to both. This, however, is of no 
consequence for the present, since I have not yet given any name to the Arran plant. 
Kather more important is the fact that M. Renault speaks of a stem having a solid 
vascular axis, like that of Lepidodendron Spenceri, to which stem he has given the 
name of L. Rhodumnense. The following description shows that it has some features 
in common with my plant:—La cavite centrale, due soit a un dechirement du tissu, 
soit a ce que le procambium n’a pas acheve sa lignification, est cylindrique, dans les 
echantillons non deformes, toujours de dimension extremement reduite, et ne presentant 
que des traces douteuses de tissu cellulaire.t Details in the structure of the cortex 
of L. Rhodumnense indicate a specific difference between it and my plant. 
The Lepidodendron intermedium, figs. 16, 17, and 18, has a special interest when 
viewed in connection with the plant which I some time ago named Lepidodendron 
fidujinosum.\ In my Memoir, Part XI.,§in Plate 49, fig. 11,1 represented a segment 
of a transverse section of the innermost, cortex of this plant, in which a very rudimen¬ 
tary exogenous vascular zone is seen at li, and in p. 290 of the Memoir I called 
attention to the liability of these vascular elements to be diverted irregularly, and in 
an undulating manner, from their straight vertical course. Fig. 17 of the present 
Memoir, show^s that thoucdi in the transverse section the vascular laminse ai’e arrano-ed 
in regular radiating lines, as is also the case in the similar section of L. faliijinosnm 
referred to above, vertical tangential sections of the same exogenous zone of L. inter- 
* Mj meaning is not made sufficiently clear in this paragraph. In its transition from being a 
segment of a circle, as in fig. 3, to becoming a perfect cylinder, as in fig. 6, the vessels composing this 
bundle must have undergone precisely such changes of relative positions as M. Renault deems impossible. 
Rut the changes have not ended here. Supposing the bundle to have supplied an ordinary latei-al branch, 
it must have become a hollow cylinder like that from which it sprang. If, on the other hand, it merely 
supplied an aborted Halouial tubercle which would be prolonged to form the axis of a Lepidostroboid 
fruit, it must have expanded in the axis of that fruit into a hollow cylinder, because all these strobili 
possess such hollow vascular cylinders, which enclose a true medulla.—September 3, 1889. 
t ‘ Cours de Botunique Fossile,’ Deuxieme annee, p. 23. 
J ‘ Proceedings of the Royal Society,’ vol. 42, p. 7. 
§ ‘Phil. Trans.,’ 1881. 
