1^8 LEPWODENDREAE. 



are given in Schimper l as mere synonyms of Lepidodendron. But as some 

 states of preservation have a different appearance from the rest, doubts are 

 still expressed as to whether they are derived from one and the same genus 

 of plants. In answer to this I would call attention once more to the fact 

 which was considered in the introductory chapter, that we must necessarily 

 see the remains of the same species under a quite different form, if it is 

 composed of portions of tissue of different power of resistance, since these 

 must have been affected by external influences in a different manner in 

 each case. A stem of this kind will have an entirely different appearance 

 in the fossil state if it rotted first of all on the damp ground in a forest, or 

 was covered by water while still fresh, or if it was exposed to the two kinds 

 of influence several times in succession. And that the first-mentioned con- 

 dition, the presence of tissues of different power of resistance, was not 

 wanting in Lepidodendrae is shown by the anatomy of these plants, which 

 will be considered presently. We may notice first the form described by 

 Sternberg 2 as Aspidiaria, Presl, which he had himself previously united 

 with Lepidodendron (Fig. 19, A). Goppert 3 has already given a complete 

 explanation of the mode of formation of these Aspidiariae, and his descrip- 

 tions have been fully confirmed by O. Feistmantel 4 , and again reviewed at 

 length by Stur 5 . When the cortical covering of the stem is removed, the 

 cushions seen from the inside form rhomboidal depressions ; whether this 

 was in consequence of the perishing of their delicate central tissue, or 

 because, as Stur thinks, there was a central lysigenetic intercellular space 

 traversed by a vascular bundle formed already during the life of the plant, 

 as in living heterophyllous Lycopodieae, is a matter of indifference and 

 cannot be determined. These hollows are filled up with the stony ma- 

 terial, and in this way flat or slightly convex lozenge-shaped areolae are 

 formed, which without further structure show the trace of the emerging 

 foliar bundle as a dot-like protuberance or an irregular central longitudinal 

 elevation, while nothing can be seen of the lateral traces. If the trace in 

 Aspidiaria is seen in the middle of the cushion, somewhat deeper therefore 

 than in the surface-picture of Lepidodendron, this is connected with the 

 ascending course of the bundle, for owing to this, the trace will appear in a 

 lower position in proportion as the surface of the cylinder bearing the im- 

 pression is further removed from the outer surface of the stem. By suitable 

 treatment of his specimen Stur has succeeded in extracting single rhombs 

 which filled the cavities, and by this means the surface of the leaf-cushion 

 was disclosed to view in its normal condition (Fig. 19, A). Schimper c gives 

 the figure of an Aspidiaria which is said to belong to Lepidodendron acule- 



1 Schimper (1). a Sternberg, Graf von (1), Heft 1-4, t. 28, and Heft 5-8, t. 68. ' Goppert 

 12), p. 48. 4 O. Feistmantel (3), p. 207; t. 40, f. i. 5 Stur (5), p. 229; t. 19, f. 4. 



5 Schimper (.1,, t. 60, f. 6. 



