160 



LECTURES 



mens. You will observe, then, the sparse dichotomous branching, the 

 cylindrical limbs with blunt extremities, so characteristic of the club- 

 moss, but which is found^ also, in some species of pines. Like the club- 

 moss, too, the leaves are crowded, pointed, strung along the stem for 

 some distance, but longer, slenderer, and more nearly resembling the 

 leaves of the pine. On this trunk you will observe the seal-like im- 

 pressions {sigilla) characteristic of this family, and from which its 

 name is derived. Also longitudinal depressions running from one 

 end of the trunk to the other, and along which the sigilla are arranged 

 in vertical rows. Thus each trunk of a Sigillaria resembled a noble 

 fluted doric ^column beautifully but variously sculptured the pattern 

 changing with the species. These sigillae are evidently leaf scars, 

 and therefore indicate the leaf arrangement peculiar to this family. 



The Lepidodendron, of which you have here a drawing, was still 

 more like the club-moss, the crowded leaves being shorter, rhomboidal, 

 and more scale like, the same long, slender, cylindrical, sparse dichot- 

 omous branches. But even here we find an almost equal resem- 

 blance to Conifers, for it will be recollected that in a large number 

 of Conifers as the Juniperus, the Araucaria, &c., the same rhomboidal, 

 j)laited scale-like leaves prevail. The impression of a shoot of an Araii- 

 caria could scarcely be distinguished from that of some species of club- 

 moss, except by superior size of the former. In its fructification there 

 is the same difficulty, for it is doubtful whether it most nearly resem- 

 bled the cone of pines, or the cone-like fructification of club-mosses, 

 although the recent investigations of Hooker leave little doubt that 

 the latter is the truer view. All that we know, then, of the external 

 appearance of these families lead us to the conclusion that they were 

 intermediate between pines and club-mosses, and that the Sigillaria 

 approached most nearly the pines, and the Lejndodendj^ons most nearly 

 the club-mosses. 



Let us next see what light is thrown upon this subject by examina- 

 tion of the internal structure. 



Fig. 24. Fi". 25. 



Cross section of Sigillaria: a the pith; h the 

 woody cylinder; c the cellular tissue; d the 

 rind; ethe bundles ot vascular tissue running 

 from central sheath to the leaves. 



Cross and longitudinal section of Sigillaria; 

 letters represent same as in fig. 24; /// the 

 leaves. 



