180 THE GEOLOGICAL HISTORY OF PLANTS. 



and which from their appearance are called "fossil 

 birds' nests " by the quarrymen. Some, however, must 

 have attained a considerable height so as to resemble 

 palms. 



The cycads, with their simple, thick trunks, usually 

 marked with rhombic scars, and bearing broad spreading 

 crowns of large, elegantly formed pinnate leaves, must 

 have formed a prominent part of the vegetation of the 

 northern hemisphere during the whole of the Mesozoic 

 period. A botanist, had there been such a person at the 

 time, would have found this to be the case everywhere 

 from the equator to Spitzbergen, and probably in the 

 southern hemisphere as well, and this throughout all the 

 long periods from the Early Trias to the Middle Cre- 

 taceous. In a paper published in the "Linnaean Trans- 

 actions" for 1868, Dr. Carruthers enumerates twenty spe- 

 cies of British Mesozoic cycads, and the number might 

 now be considerably increased. 



The pines present some features of interest. We have 

 already seen their connection with the broad-leaved Cor- 

 daites, and in the Permian there are some additional 



types of broad -leaved coniferae. 

 In the Mesozoic we have great 

 numbers of beautiful trees, 

 with those elegant fan-shaped 

 leaves characteristic of but one 

 living species, the Salisburia, 

 or gingko-tree of China. It is 

 curious that this tree, though 

 now limited to eastern Asia, 

 will grow, though it rarely 

 fruits, in most parts of tem- 

 perate Europe, and in America as far north as Montreal, 

 and that in the Mesozoic period it occupied all these re- 

 gions, and even Siberia and Greenland, and with many 

 and diversified species (Fig. 66). 



Fia. 66. — Salisburia (Gingko) 

 Sibirica, Heer. L. Creta- 

 ceous, Siberia and North 

 America. 



