GINKGOALES 



215 



Where weather conditions are about the same as in Chicago and 

 northern Ohio, scarcely any seedlings grown in the open survive 

 the first winter. They should be kept in the greenhouse the first 

 winter, put out in the spring after frosts are over but while the 

 weather is still cool, and then 

 taken in after the first light 

 frost in autumn. By putting 

 them out earlier and earlier in 

 the spring, and taking them in 

 later and later in the autumn, 

 for four or five years, they be- 

 come hardened so that many 

 will survive the winters. Even 

 where there is some snow and 

 ice, but not such severe cold as 

 in the Chicago region, a consid- 

 erable proportion of the seed- 

 lings survive without any such 

 precautions. 



PHYLOGENY 



How far back into geological 

 times the Ginkgoales extend 

 depends upon the interpreta- 

 tion of leaves which may or 

 may not belong to this group. 

 It is certain that as far back as 

 the Lower Permian it was 

 abundant and widely distrib- 

 uted. Baiera, some of the spe- 

 cies of which can scarcely be 



excluded from the genus, Ginkgo, was abundant in the Lower Per- 

 mian. In the Carboniferous, only leaves have been found, but they 

 seem to belong to Ginkgoales rather than to Cordaitales. All of 

 the order, except one species of Ginkgo, have been extinct since the 

 Upper Jurassic, and many think that even the one species is extinct, 

 except as it is kept alive by cultivation. 



Fig. 232. — Ginkgo biloba: seedlings, bear- 

 ing a general resemblance to those of cycads, 

 or of Quercus. — From Coulter and Cham- 

 berlain, Morphology of Gymnosperms'^ 

 (University of Chicago Press). 



