370 GEADE OF THE CAEBONIFEEOUS FLOEA. [Ch. XXIV 



limestone. The sandstone, ironstone, shales, and coal itself, all contain 

 them. Mr. Binney has at length found in the clay-ironstone of Lanca- 

 shire several specimens displaying structure, and from these, says Dr. 

 Hooker, we learn that the Trigonocarpon belonged to that large section 

 of existing coniferous plants which bear fleshy solitary fruits, and not 

 cones. It resembled very closely the fruit of the Chinese genus Salisburia, 

 one of the Yew tribe, or Taxoid conifers. In five of the fossil specimens 

 there is evidence of four distinct integuments, and of a large internal 

 cavity filled with carbonate of lime and magnesia, and probably once 

 occupied by the albumen and embryo of the seed. The general form of 

 the fossil when perfect is an elongated ovoid, rather larger than a hazle- 

 nut. The exterior integument is very thick and cellular, and was no 

 doubt once fleshy (see fig. 487). It alone is produced beyond the seed, 

 and forms the beak. The second coat was thinner, but hard, and marked 

 by 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 membranes, and 

 may possibly have been two plates belonging to one membrane. 



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

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

 sive modifications of elementary organs for the purpose of their adaptation 

 to special functions, and these modifications are as great, and the adapta- 

 tion as special, as any to be found amongst analogous fruits in the ex- 

 isting vegetable world."* Professor Williamson, in his paper on Stern- 

 bergia, 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 de- 

 serve notice, because a question has arisen — whether the Coniferos hold 

 a high or a low position among flowering plants, — a point bearing 

 directly on the theory of progressive development. By some botanists 

 all the Gymnospermous Dicotyledons are regarded as inferior in grade 

 to the Angiosperms. Others hold, with Dr. Hooker, that the Gymno- 

 sperms are not inferior in rank, having every typical character of the 

 dicotyledons highly developed. Thus Coniferae have flowers, and are 

 propagated by seeds which are developed through the mutual action of 

 the stamens and ovules ; they have distinct embryos, and germinate in a 

 definite manner. 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 structural development. The 

 Coniferae are exogenous, and have the same distinctions of pith, wood, 

 bark, and medullary rays as have the angiospermous trees. Whether 

 the woody fibre with disks characteristic of Coniferae be a more or a 

 less complex tissue than the spiral vessels, is a controverted point. As 

 '.he spiral vessels occur in the young shoots, and are lost in the mature 



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



