SUBKINGDOM SPERMATOPHYTA 



331 



borne upon small sporophylls arranged upon slender spikes. The 

 germination of the pollen-spores, and the development of motile sper- 

 matozoids, is the same as that of the Cycads, and the development of 

 the embryo is similar. 



The histology of the stem of the older sporophyte, however, is 

 more like that of the Coniferse. 



Geological History of Ginkgo. Ginkgo is, even more than the 

 Cycads, a left-over type. Forms undoubtedly related to Ginkgo 



FIG. 293. Ginkgo biloba. Branch of a fruiting tree, reduced. (After BAILEY.) 



occur in the later Carboniferous, and during the late Palaeozoic and 

 early Mesozoic Ages, the order was represented by numerous species. 



Order III. Coniferae 



Much the greater number of existing Gymnosperms belong to the 

 Coniferae, which include all the familiar " evergreen " trees of the 

 northern forests. The sporophyte may reach gigantic dimensions 

 and live many hundreds of years. Several species of the Pacific 

 coast forest attain a height of over one hundred metres, with a stem- 



