292 W. Carrut/iers — The Forests of the Coal Period. 



leaves are simple, and arranged spirally on the stem. The branches 

 are irregular and dichotomous. 



The fruit is produced in terminal cones composed of imbricating 

 scales. Each scale bears on its pedicel a small sporangium full of 

 spores. In Selaginell^ two kinds of spores exist. The one, called 

 microspores, produces spermatozoids ; the other, macrospores, germi- 

 nates, and forms a prothallus on which pistillidia appear ; and these, 

 when fertilized by the spermatozoids of the microspores, grow into 

 perfect plants. In Lycopodium microspores only have been seen, and 

 the process of its germination is still unknown. 



The little Quillwort (Isoetes) which grows at the bottom of most 

 of our mountain lakes, agrees with Selaginella in having two kinds of 

 spores ; but it differs from the true club-mosses in its habit and in 

 the structure of the stem. Like Welwitschia it never increases in 

 height ; but this is even more remarkable in the Quill-wort than in 

 Welwitschia, seeing that in it there is, as long as the plant lives, a 

 continual development of nodes with their foliar appendages going 

 on. The axis of the stem is composed of cellular tissue. This is 

 surrounded by a vascular cylinder, which grows, as in exogens, by 

 the addition of external layers, there being in this plant a true 

 cambium layer outside the wood, a structure imknown in other 

 cryptogams. 



IV. No plants allied to the Pillworts have hitherto been detected 

 in the Coal Measures ; we need not, therefore, be detained by an 

 examination of their structure and development. 



In examining the palaeozoic cryptogams of the Coal Forests, I 

 will follow the same order as that in which we have glanced at 

 their living representatives. 



I. The Ferns need not long occupy our attention. They were 

 very abundant, though as a rule they were humble herbaceous 

 plants. Arborescent stems are extremely rare — only two undoubted 

 species have been met with in Britain. The numerous known forms 

 have either grown on the earth, or, as is very probable, been 

 Epiphytes. Fructification is rare ; in the few cases in which it has 

 been found it agrees with that of recent ferus. Occasionally young 

 fronds exhibiting circinnate vernation have been met with, showing 

 that this method of unrolling the frond was as characteristic of the 

 ferns of that period as it is of those of the present. 



The fern is a remai-kably stable type of vegetation. The earliest 

 forms, like the Cyclopteris Hihernica of Forbes from the Old Eed 

 Sandstone, agrees in all comparable points with the recent plants ; 

 and throughout all the intervening space no divergence in any point 

 of importance has been detected. 



II. No group of fossil plants can more fully illustrate the imper- 

 fect materials with which the paleeontological botanist has to deal 

 than that group which I have united under the name Calamites} The 

 various parts of the plant — the root, the stem, the leaves, and the 



1 On the Structure of the Fruit of Calamites. Seeman's Joui-nal of Botany, vol. v. 

 (1867), p. 349, PI. 70. 



