TRANSACTIONS OF SECTION C. 483 
discovered that it occurred equally in many small plants like Sphenophyllum, Astero- 
phyllites and other more diminutive types. 
After thirteen years of persevering demonstration, these views, at first so 
strongly opposed, have found almost universal acceptance. Nevertheless, there 
‘still remain some few who believe them to be erroneous. In the later stages of 
this discussion the botanical relations subsisting between Lepidodendron, Sigillaria, 
and Stigmaria have been the chief themes of debate. In this country we regard the 
conclusion that Stigmaria is not only a root, but the root alike of Lepidodendron 
and Sigillaria, as settled beyond all dispute. Nevertheless M. Renault and M. 
Grand-Eury believe that it is frequently a leaf-bearing rhizome, from which 
aerial stems are sent upwards. I am satisfied that there is not a shadow of founda- 
tion for such a belief. The same authors, along with their distinguished country- 
man, the Marquis of Saporta, believe, with Brongniart, that it is possible to sepa- 
rate Sigillaria widely from Lepidodendron. They leave the latter plant amongst 
the Lycopods, and elevate the former to the rank of a Gymnospermous Exogen. I 
have demonstrated in vain the existence of a large series of specimens of the same 
species of plant, young states of which display all the essential features of structure 
which they believe to characterise Lepidodendron, whilst in its progress to matu- 
rity, every stage in the development of the secondary wood, regarded by them as: 
characteristic of a Sigdlaria, can be followed step by step.! Nay, more: my cabi- 
net contains specimens of young dichotomously branching twigs, in which one of 
the two diverging branches has only the centripetal cylinder of the Lepidodendron, 
whilst the other has begun to develop the secondary wood of the Sigillaria.? 
: The distinguished botanist of the Institut, Professor Ph. van Tieghem, has recently 
paid some attention to the conclusions adopted by his three countrymen in this. 
controversy, and has made an important advance upon those conclusions, in what 
I believe to be the right direction. He recognises the Lycopodiaceous character of 
the Sigillarie, and their close relations to the Lepidodendra ;* and he also accepts 
my demonstration of the unipolar, and consequently Lycopodiaceous, character of 
the fibro-vascular bundle of the Stigmarian rootlet, a peculiarity of structure of 
which M. Renault hes hithero denied the existence. But, along with these recog- 
nitions of the accuracy of my conclusions, he gives fresh currency to several of the 
old errors relating to parts of the subject to which he has not yet given personal 
attention. Thus he considers that the Sigillarie, though closely allied to the 
Lepidodendra, are distinguished from them by possessing the power of developing: 
the centrifugal or exogenous zone of vascular tissue already referred to. He charac-. 
terises the Lepidodendra as having ‘ un seul bois centripéte, notwithstanding the ab-- 
solute demonstrations to the contrary contained in my Memoir xi. | Dealing with: 
the root of Stgillaria, which in Great Britain at least is the well-known Stigmaria 
Jicoudes, following Renault, he designates it a ‘rhizome,’ limiting the term root 
to what we designate the rootlets. He says, ‘Le rhizome des Sigillaires a la 
méme structure que la tige aérienne, avec des bois primaires tantét isolés 4 la 
périphérie de la moelle, tantét confluents au centre et en un axe plein; seulement 
les fasceaux libéro-ligneux secondaires y sont séparés par de plus larges rayons,’ &e. 
Now, Stigmaria being a root, and not a rhizome, contains no representative of 
the primary wood of the stem. This latter is, as even M. Brongniart so correctly 
pointed out long ago, the representative of the medullary sheath, and the fibro-vas- 
cular bundles which it gives off are all foliar ones, as is the case with the bundles 
given off by this sheath in all Exogenous plants. But in the Lepidodendra and 
Sigilarie, as in all living exogens, it is not prolonged into the root. In the latter, 
as might be expected @ priort, we only find the secondary, or exogenous, vascular zone. 
Having probably the largest collection of sections of Stigmariz in the world, I speak 
unhesitatingly on these points. M. van Tieghem further says, ‘ La tige aérienne part 
@un rhizome rameux trés-développé nommé Stigmaria, sur lequel s’insérent & la fois 
de petites feuilles et des racines parfois dichotomées,’ I have yet to see a solitary 
fact justifying the statement that leaves are intermingled with the rootlets of 
1 Memoir xi. Plates xlvii.—lii, ? Idem, Pl. xlix. fig. 8. 
3 Traité de Botanique, p. 1304. 
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