332 Eevieics — Dawson's Acadian Geology. 



monstration of their relations ; but the only method of determining 

 with certainty the diiferent parts of a vegetable organism is the 

 discovery of these parts in organic connection. Thus in Sigillaria, 

 as long as we know that it had a long fluted and scarred trunk and 

 stigmaria root, and only this, we may restore it as a simple, dichoto- 

 mous branching, or irregularly and repeatedly branching stem 

 covered v/ith small, long, or fern-like leaves ; and each of these, as 

 far as the materials over which our restoration is based, with equal 

 accuracy. 



The most curious restoration in the volume is that of MegapJiyton, 

 (Fig. 1) of which genus all that we know is that it had a large trunk 

 with two opposite rows of large reniform or oval scars and numerous 

 smaller scars covering the rest of the stem. This Dr. Dawson 

 restores as a tree-fern bearing opposite pairs of enormous fronds. 

 We cannot imderstand how the vascular tissue was developed to 

 form so large a stem when the leaves were far removed on the 

 opposite surfaces, and their bases not amplexicaul. So opposed is 

 this to what is known in any recent plant that we prefer, with M. 

 Ad. Brongniart, to consider the large scars as produced by branches, 

 by peduncles, or by adventitious roots, rather than by leaves, and to 

 place Megaphyton along with Ulodendron as an ally of Lejndodendron. 



In the restoration of Calamites we believe there is reason for going 

 further than is done in Fig. 2. The structure and arrangement of 

 the fruit and the foliage in AsteropJiyllites, Annularia, and Spheno- 

 phjllum are the same. Their remains are associated with those of 

 Calamodendron, and when the structure of the stem is preserved it is 

 found to be the same as that of this genus. Dr. Dawson has himself 

 observed this, for in speaking of AsteropJiyllites, he says that they 

 had a " stout internal woody cylinder, in which respect they re- 

 sembled miniature Calamodendra.'' The ribs on the stems were 

 internal in the branches known as AsteropJiyllites just as in Calamo- 

 dendron. The vascular bundles were parallel in the internodes, but 

 interlaced at the nodes as in Equisetum, and the whorl of scars ( A^ and 

 A^) associated with the interlacings at the nodes represent the open- 

 ing of the meshes through which the vascular bundles passed to the 

 whorl of leaves or branches produced at the nodes. Nothing is 

 known of Calamodendron by those who retain it as a distinct genus, 

 but that it was a stem ; associated with it are these branches, leaves, 

 and fruit, which agree in structure with it — and that they actually 

 belonged to it can scarcely we think be doubted. The fruit was 

 certainly that of a cryptogam belonging to the Order Equisetacece — 

 but to this is opposed the statement that disc-bearing tissue charac- 

 teristic of gymnosperms enters into the composition of the stem of 

 Calamodendron. We have carefully examined several beautiful 

 stems belonging to Mr. Binney, and a large series of our own from 

 the Ash-bed in Arran, but have failed to detect any disc-bearing 

 tissue. The whole vascular portion of the stem is made up of 

 Bcalariform tissue, as in the larger number of vascular cryptogams, 

 but differing in this respect remarkably from the recent Equisetacece 

 It would greatly add to the value of Dr. Dawson's restorations and 



