478 GEADE OF THE CARBONIFEROUS FLORA. [Ch. XXIY. 



three ridges. This coat, being all that commonly remains in a fossil 

 state, has suggested the name of Trigonocarpon. Within this were 

 the third and fourth coats, both of which are very delicate mem- 

 branes, and may possibly have been two plates belonging to one mem- 

 brane. 



Grade of the Carboniferous Flora. — On the whole, these fruits, says 

 Dr. Hooker, are referable to " a highly developed type, exhibiting ex- 

 tensive modifications of elementary organs for the purpose of their 

 adaptation to special functions, and these modifications are as great, 

 and the adaptations as special, as any to be found amongst analogous 

 fruits in the existing vegetable world." * Professor Williamson, in 

 his paper on Stembergia, has likewise remarked that its structure was 

 complex, and that " at a period so early as the carboniferous all the 

 now-existing forms of vegetable tissue appear to have been created." 

 These observations deserve notice, because a question has arisen, 

 whether the Coniferce hold a high or a low position among flowering 

 plants — a point bearing directly on the theory of progressive develop- 

 ment. By some botanists all the Gyrunospermous Dicotyledons are 

 regarded as inferior in grade to the Angiosperms. Others hold, with 

 Dr. Hooker, that the Gymnosperms are not inferior in rank, having 

 every typical character of the dicotyledons highly developed. Thus 

 Coniferse have flowers, and are propagated by seeds Avhich are developed 

 through the mutual action of the stamens and ovules ; they have dico- 

 tyledonous and polycotyledonous embryos, and germinate in the same 

 manner as other dicotyledons. The seed-vessel (or ovary) is not closed, 

 but this is also the case in some genera of angiosperms, in which 

 the ovary is open before or after impregnation, so that this character 

 cannot be relied on as constituting a fundamental difference in struc- 

 tural development. The Coniferse are exogenous, and have the same 

 arrangement of pith, wood, bark, and medullary rays as have the typical 

 dicotyledonous trees. Whether the woody fibre with discs character- 

 istic of Coniferse be a more or a less complex tissue than the spiral ves- 

 sels, is a controverted point. As the spiral vessels occur in the young- 

 shoots, and are lost in the mature growth of some plants, and as they 

 appear in many acrogens, they do not seem to mark a high develop- 

 ment. In fine, there is much ambiguity in deciding what should or 

 should not be called high or low in vegetable structure, and physi- 

 ologists entertain very different abstract ideas as to the perfection of 

 certain organs and their relative functional importance, even where the 

 function is clearly ascertained. It is enough for the geologist to know, 

 that fossil Coniferae abound in the oldest rocks, yielding a considerable 

 number of vegetable remains, and that plants of this order lay claim, 

 if not to the highest, at least to so high a place in the scale of vegeta- 

 ble life, as to preclude us from characterizing the carboniferous flora 

 as consisting of imperfectly developed plants. 



* Proceedings of the Royal Society, vol. vii., March, 1854, p. 28. 



