296 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
either as regards bark, leaves, or roots. I would further call attention to the fact that, 
so far as externals are concerned, the fine Lycopodium ulicifolium recently imported 
from Ivhasia Hills in northern India in a living state, only requires to be raised upon 
an arborescent stem to furnish an exact copy of the ancient Lepidodendra . Its thick, 
succulent, dependent branches, devoid of all adventitious roots; its oblong, flat, 
spirally-arranged leaflets, which leave, when they fall, a distinct Lepidodendroid 
cicatrix ; and its huge, often dichotomous, strobili, usually six inches in length, remind 
us most vividly of the dependent branches of the Palaeozoic Lycopods. 
The successive developments of the various vegetable elementary tissues is not 
unimportant. The modification of spiral tissue known as the “ barred” vessel—the 
“ vaisseau raye ” of the French Palseo-botanists, and which approximates closely to 
the modern “ scalariform ” tissue—has long been known to be the prevalent vascular 
element amongst Palaeozoic plants. Either in its ordinary shape, or in its “ reticu¬ 
lated ” modification, it is common to the Catamites, the Sphenophyllums, the Astc.ro- 
phyllites, and the Lyginodendra. Amongst our British Lepidodendra we have as yet 
found only the simple barred form ; and this statement applies not only to the plants 
recognised by my opponents as Lycopodiaceous, but also to those Diploxyloid ones for 
which they claim Gymnospermous rank. 
It is a fact of some importance that I have failed to detect in any one of our 
British fossil Lepidodendroids (including Sigillarice ) a trace of those fibres with 
areolated “ margined pits ” which exist abundantly in all living Cyoads, in which 
latter, as I showed long ago,'”' modifications of the spiral and the pitted states can 
be discovered in the same individual vessel.t 
But M. It ex ault has discovered in France an important group of carboniferous 
plants which undoubtedly possess the barred and areolated tissues in the same 
stems, to which group he has given the name of Poroxylees; as he points out, these 
Poroxylons appear to connect the Sigillarice. on the one hand with the Gymnospermous 
Cordaites on the other.]; This very important discovery, the reality of which there 
is apparently no reason to doubt, unquestionably links the Palaeozoic Lycopodiacece to 
the Gymnosperms of the same age, so far as elementary structures are concerned, as 
completely as any Evolutionist need desire. The arrangement of these elementary 
tissues into vegetative organs leads us to the same conclusion. The ample develop¬ 
ment of an exogenous vascular zone in true Cryptogams is demonstrated in the preceding 
pages as well as in my previous memoirs. In the young Lepidodendron the centri¬ 
petal representative of the vascular medullary sheath, which even Brongniart 
recognized as an “ etui medullaire,” is not only enormously large, but it is the sole 
* “ On the Structure and Affinities of some Exogenous Stems from the Coal-measures,” ‘ Monthly 
Microscopical Journal,’ Aug. 1, 1869. 
f It must not be forgotten that Dr. Dawson considers that he has discovered this tissue associated with 
barred vessels in some of the Canadian Sigillarice. 
J Loc. cit., p. 273. 
