134 THE GEOLOGICAL HISTORY OF PLANTS. 



of connection between the higher cryptogams and the 

 phaenogams, one leading from the lycopods by the Sigil- 

 lariaB, another leading by the Cordaites, and the third 

 leading from the Equisetums by the Calami tes. Still 

 further back the characters afterward separated in the 

 club-mosses, mare's-tails, and ferns, were united in the 

 Khizocarps, or, as some now, but I think somewhat un- 

 reasonably, prefer to call them, the " heterosporous Fili- 

 cinae." In the more modern world, all the connecting 

 links have become extinct and the phaen ogams stand 

 widely separated from the higher cryptogams. I do not 

 make these remarks in a Darwinian sense, but merely to 

 state what appear to be the lines of natural affinity and 

 the links wanting to give unity to the system of nature. 



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 cer- 

 tainly 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 cor- 



