Of all the trees of the modern world, none are perhaps so widely distributed as the pines and their allies. On mountain-tops and within the Arctic zone, the last trees that can struggle against the unfavourable conditions of existence are the spruces and firs, and in the warm and moist islands of the tropics they seem equally at home with the tree-ferns and the palms. We have already seen that they are a very ancient family, and in the sandstones of the coal-formation their great trunks are frequently found, infiltrated with calcareous or silicious matter, and still retaining their structure in the greatest perfection (Fig. 60). So far as we know, the foliage of some of them which constitutes the genera _Walchia_ and _Araucarites_ of some authors (Figs. 60, 63) was not dissimilar from that of modern yews and spruces, though there is reason to believe that some others had broad, fern-like leaves like those of the gingko. None of them, so far as yet certainly known, were cone-bearing trees, their fruit having probably been similar to that of the yews (Fig. 61). The minute structures of their stems are nearer to those of the conifers of the islands of the southern hemisphere than to that of those in our northern climes--a correlation, no doubt, to the equable climate of the period. There is not much evidence that they grew with the Sigillariæ in the true coal-swamps, though some specimens have been found in this association. It is more likely that they were in the main inland and upland trees, and that in consequence they are mostly known to us by drifted trunks borne by river inundations into the seas and estuaries. [Illustration: Fig. 60.--Coniferous wood and foliage (Carboniferous). A, _Araucarites gracilis_, reduced, b, _Dadoxylon Acadianum_ (radial), 90 diams.; B^1 (tangential), 90 diams; B^2, cell showing areolation, 250 diams. C, _Dadoxylon materiarium_ (radial), 90 diams.; C^1 (tangential), 90 diams. C^2, cell showing areolation, 250 diams. D, _Dadoxylon antiquius_ (radial), 90 diams.; D^1 (tangential), 90 diams.; D^2, cell showing areolation, 250 diams.] [Illustration: Fig. 61.--__Trigonocarpum Hookeri_, Dawson from the coal-measures of Cape Breton. Probably the fruit of a Taxine tree. A, Broken specimen magnified twice natural size, B, Section magnified: _a_, the testa; _b_, the tegmen; _c_, the nucleus; _d_, the embryo, _c_, Portion of the surface of the inner coat more highly magnified.]