of the Fossil Plants of the genus Sigillaria, 273 



furrowed, more or less in a longitudinal direction — a peculiarity which is 

 produced by the elongation and arrangement of the leaf-bases. This is 

 particularly obvious in a specimen of the larch, of which a sketch a 

 little above the natural size is given in fig. 1 (PI. IV.) In this specimen, 

 the leaf-bases a, a are connected with each other by threads of cuticle (6) ; 

 by this means a number of such connected leaf-bases forms, as it were, a 

 linear series, which, when traced for any distance on the surface of the 

 stem, will be found to coil round its axis in spirals, whose volutions are 

 very much apart. The direction of the spirals thus traceable is, in this 

 instance, to the left, that is, when looking upon them ; but this does 

 not appear to be constant, for in some specimens of the same plant at 

 present before me, the spirals run in the opposite direction ; irregulari- 

 ties of growth obviously induce this difference. From an examination 

 of a number of specimens, I do not, however, hesitate to say, that the 

 general direction of these spirals is to the left.* 



I am not aware that the manner in which I have shewn the leaf-bases 

 to be connected with each other has been mentioned by botanists — even 

 by those who have written on the spiral arrangement of the leaves, and 

 other appendages of the stem, or other axes. Can it be, that in each 

 linear series or spiral, we have the course which the constituent vessels 

 of a single system of leaves fall into, as they are developed, and as they 

 strike off from the medullary sheath } 



Were it not that the threads of cuticle connect the leaf-bases toge- 

 ther, the species of larch which is figured would present a striking 

 analogy to Sigillaria, as respects the ribs and furrows. Another Coni- 

 ferous species, hereafter to be noticed, offers a still closer agreement. 



As bearing on the subject under consideration, it may be mentioned, 

 that, in Lepidodendron, the lozenges or leaf-bases, which give such a re- 

 markable appearance to this fossil, are resolvable into spirals, whose 

 volutions may occasionally be traced by the same means as I have pointed 

 out in the case of the larch. In the outline given in figure 2 (PI. IV.)^ 

 two sets of spirals, corresponding to the leaf-bases a, a, and 6, h may 

 be traced, either of which might be taken for the true one, because of the 

 absence of connecting threads of cuticle. t In the other specimen (Fig. 3, 

 PI. v.), however, we have not this diflSculty to contend against, for the 



♦ The volution of such spirals on the stems of Conifera, appears to follow the 

 same direction as that of the spiral fibres in vascular tissue. According to Mohl, 

 these fibres are in general wound to the right, that is, their volutions are such, 

 that, to an observer placed in the axis of the cylinder around which the fibres 

 rise, the spiral mounts from left to right. — Vide a paper by Mohl on the struc- 

 ture of annular vessels, translated in the " Annals of Natural History," vol. viii. 



t This specimen exhibits, in a very decided manner, the axillary buds men- 

 tioned in a former part of this paper. I have given an enlai'ged outline of a 

 lozenge in figure 2 x, in which the prominence a represents the axillary bud : the 

 other parts of this lozenge I hope to be able to explain in a paper which I 

 intend to publish on Lepidodendron. 



