TRANSACTIONS OF SECTION C. 485 
comes quite as conspicuous as the vertical one. This is the case even in Brongniart’s 
classic specimen of Stgillaria elegans, long the only fragment of that genus known 
which retained its internal structure. ‘The fact is, the shape of the leaf-scars, as 
well as the degree of their proximity to each other, underwent great changes as 
Lepidodendroid and Sigillarian stems advanced from youth to age. Thus Presl’s genus 
Bergeria was based on forms of Lepidodendroid scars which we now find on most of 
the terminal branches of unmistakable Lepidodendra.' The phyllotaxis of Stgillaria, 
of the type of S. occulata, passes by imperceptible gradations into that of 
Favularia, In many young branches the leaves were densely crowded together ; 
but the exogenous development of the interior of the stem, and its consequent 
growth both in length and thickness, pushed these scars apart at the same time 
that it increased their size and altered their shape. We see precisely the same 
effects produced by the same causes upon the large fruit-scars of Ulodendron. The 
Carboniferous Lycopods were mostly arborescent, but some few dwarf forms, 
apparently like the modern Selaginelle, have been found in the Saarbriicken coal- 
fields. Many of the arborescent forms, if not all, produced secondary wood, by means 
of a cambium layer, as they increased in age. In the case of some of them ® this 
was done in a very rudimentary manner, nevertheless sufficiently so to demonstrate 
what is essential to the matter, viz. the existence of a cambium layer producing a 
centrifugal growth of secondary vascular tissue. 
As already pointed out in the case of the Calamites, the vascular axis of these 
Lepidodendra was purely an appareil conducteur, unmixed with any wood-cells; 
hence the apparetl de soutien had to be supplied elsewhere. This was done in the 
same way as in the Calamites: a thick, persistent, hypodermal zone of meristem * 
developed a layer of prismatic prosenchyma of enormous thickness,* which encased 
the softer structures in a strong cylinder of self-supporting tissue. We have positive 
evidence that the fructification of many of these plants was in the form of 
heterosporous strobili. Whether or not such was the case with all these Lepidostrobi 
we are yet unable to determine. But the incalculable myriads of their macrospores, 
seen in so many coals, afford clear evidence that the heterosporous types must have 
preponderated vastly over all others. 
Gymmnosperms.—Our knowledge of this part of the Carboniferous vegetation 
has made great progress during the last thirty years. This progress began with my 
own discovery * that all our British Dadoxylons possessed what is termed a discoid 
pith, such as we see in the white Jasmine, some of the American hickories, and 
several other plants. At the same time I demonstrated that most of our objects 
hitherto known as Artistas and Sternbergias were merely inorganic casts of these 
discoid medullary cavities. Further knowledge of the genus Dadoxylon seems to 
suggest that it was not only the oldest of the true Conifers in point of time, but also 
one of the lowest of the coniferous types. 
Cycads.—The combined labours of Grand-Eury, Brongniart, and Renault have 
revealed the unexpected predominance, in some localities, of a primitive but varied 
type of Cycadean vegetation. Observers have long been familiar with certain seeds 
known as 7?tgonocarpons and Cardiocarpons, and with large leaves to which the 
name of Noeggerathia was given by Sternberg. All these seeds and leaves have 
been tossed from family to family at the caprice of different classifiers, but in all 
cases without much knowledge on which to base their determinations, The rich 
mass of material disinterred by M. Grand-Eury at St. Etienne, and studied by 
1 See Memoir xii. Pl. xxxiv. 
2 Bg. Lu. Harcourtii, Memoir xi. Pl. xlix. fig. 11. 
3 Memoir ix. Pl. xxv. figs. 93, 94, 98, 99, 100, and 101. 
4 Memoir xi. Pl. xlviil. fig. 4f7’. Memoir ii. Pl. xxix. fig. 422. Memoir iii. Pl. 
xliii. fig. 17. 
5 «On the Structure and Affinities of the Plants hitherto known as Sternbergias,’ 
Memoirs of the Literary and Philosophical Society of Manchester, 1851. M. Renault, 
in his Structure comparée de quelques Tiges de la Flore Carbonifere, p. 285, has erro- 
neously attributed this discovery to Mr. Dawes, including my illustration from the 
_Jasminium and Juglans. Mr. Dawes’ explanation was a very different one. 
