ON COAL. 163 



mature condition, except in the family of club-mosses. In tlie embry- 

 onic state, however, of the Dicotyledons we find something similar. 

 If we make a cross section of a Dicotyledon soon after germination, 

 t. e., while the first two or three pairs of leaves are expanding, we will 

 find a structure very similar to that of the Lepidodendron. We find 

 in the centre a small pith surrounded by a thin zone of vascular tissue, 

 (mostly spiral vessels,) around this a large mass of cellular tissue, des- 

 tined to become partly bark and partly wood_, but which is yet neither 

 one nor the other, and the whole inclosed in a thin epidermis of con- 

 densed cellular tissue. 



Thus it appears, both from external and internal examination, that 

 these families combined the characters of pines and club-mosses. Or 

 if we are disposed to attach moro importance to their exogenous affini- 

 ties, and thus to place them among the pines, then we must compare 

 them with the earliest embryonic condition of this class. The true 

 view, I am convinced, is, that they are both connecting and embryonic 

 types, or connecting types with embryonic characters. In fact, all 

 embryonic types seem to be more or less connecting, and conversely 

 connecting types, at least in Falceontology, are also embryonic. Now, 

 what I have said of the Sigillaria and Lepidodendron is equally true, 

 I believe, of other coal plants. I have taken these two because they 

 are better known ; but all that is known concerning other genera 

 seem to point in the same direction. They all seem to be more or less 

 connecting types. The Sphenophyllum, Noggerathia, and probably 

 many of the so-called Ferns of this period are of this character. 



Let us inquire now what important conclusions may be drawn from 

 what we have seen of the affinities of these plants : 



1. The distinction of plants into Cryptogams and Phcenogams is 

 considered by botanists a fundamental one. Many recent investiga- 

 tions, however, have combined to throw some doubt upon the entire 

 distinctness of these classes. The study of the Coal Plants, particu- 

 larly of the two families Sigillaria and Lepidodendron , it seems to me 

 entirely destroys this as a fundamental division, or, at least, as one at 

 all comparable to the great divisions of the animal kingdom. The 

 pines belong uaequivocally to the Phcenogams and the club-mosses to 

 the Cryptogams. If the Sigillaria and Lepidodendron are connecting 

 links between these two families then the classes to which they belong 

 can no longer be considered as fundamentally distinct types or plans 

 of structure. The study of animals, both existing and extinct, have 

 confirmed the wonderful generalization of Cuvier. The four types — 

 Vertebrata, Articidala, 3IoUusca, and Radiata — were as distinct during 

 the palaeozoic period as now. If such distinct plans of structure 

 exist in the vegetable kingdom at all they have not yet been indicated 

 as such by botanists. The distinction into exogen and endogen would 

 seem more likely to be fundamental, as this is apparently not a mere 

 distinction of rank or complexity of structure, but of plan of struc- 

 ture. If 80, then we shall probably be able to trace these two types 

 downwards until, overleaping the distinction of Phcenogams and 

 Cryptogams as one of complexity of structure only, they reach the 

 lower confines of the vegetable kingdom. 



2. We have seen that the plants of the coal are most_, if not all of 



