OF THE FOSSIL PLANTS OF THE COAL-MEASUKES. 
201 
branches of ray Arran Lejndodendi'on were supplied, as in fig. 1, by large segments 
cut off from the solid vascular bundle which, in the young branches of that plant, 
represents the medullary vascular cylinder of its older stem. 1 have also in my 
cabinet a section of the Burntisland Lepidodendron (cabinet number .502) which is 
giving off a similar branch. Various other specimens, of a like character, that have 
come under my notice, suggest the conclusion that the ordinary ramification of these 
Lepidodendra was dichotomous, as in fig. 25 of the present Memoir; but that, where 
a branch was of a special kind, characterised by an arrested development, then the 
mode of branching illustrated by figs. 1-5 was the normal one. It has long been 
certain that the scars of t//ocA?mZron represent such arrested branches, which supported 
Lepidostrobi; and it is iu the liighest degree probable that the tubercles of Ilalonia 
are similar organs. A memoir by Mr. Kidston* clearly demonstrated that Ulodevdron 
is not a genus of plants, but merely a condition of various Lepidodendroid genera; 
and the remark is equally applicable to the name Ilalonia, which, as is shown in 
Plate 34 of my Memoir, Part XII. (‘Phil. Trans.,’ Part. II., 1883), represents the 
extremities of an ordinary Lepidodendroid branch. A fine specimen of Ilalonia 
regularis in my cabinet shows that the ordinary branching of Halonial forms is dicho¬ 
tomous, as in fig. 14. It is therefore obvious that branches like figs. 1-5 represent 
some special ramification, distinct from the normal dichotomous one ; and the only 
possible explanation that I can discover is that such arrested or subordinate branches 
were destined to support strobili. 
It cannot now be doubted that the strobili of Lepidodendron were affixed to their 
sustaining branches in two ways. In one fine Lepndostrohus in my collection the base 
of the strobilus terminates the extremity of a long, slender pendulous twig. But in 
another very fine example, in the Museum of the Owens College, the large Lepido- 
strobus is planted laterally in an almost sessile manner upon a strong branch. In 
this instance the strobilus is evidently sustained by a short, arrested lateral twig, 
corresponding to one of the Halonial tubercles. The sections, figs. 1, 5, further 
establish another morphological fact, viz., that the young branches of a Lepido¬ 
dendron may have a vascular bundle devoid of all visible traces of a cellular medulla, 
and yet such a medulla may be developed in its interior at a later stage of growth. 
In some of .my earlier memoirs I advanced the hypothesis that age produced 
other morphological changes, beyond mere growths, in these Lepidodendroid plants. To 
this M. Benault replied, speaking of L. Ilarcoiirtii, “ On pent done conclure Cjiie la 
difference de diametre des rameaux de Lepidodendron n’apporte pas de changements 
dans la disposition generate des tissus qui les composent.”t 
My sections of L. Ilarcourtii demonstrate that such changes do occur; since, as 
the section, fig. 1, shows at a, the older and larger branches possess a very large 
medulla, which exists in like manner in all the older Halonial branches, which certainly 
* “ On the Relationships of JJlodenrlron'’ ‘ Ann. Mag. Nat. Hist.,’ vol. 16, 1885. 
t ‘ Cours de Botanique Fossile,’ Deuxieme annee, p. 28. 
MDCCCLXXXIX. —B. 2 D 
