232 HEREDITY AND EVOLUTION IN PLANTS 



the perianth an ancient structure, present in the ancestors 

 of the Angiosperms, and inclosing an axis (" amphispor- 

 angiate cone") bearing both megasporophylls and micro- 

 sporophylls. Such a structure is called by Arber an 

 "anthostroMlus." The term "flower," should be re- 

 stricted to Angiosperms, and may be termed an "eu- 

 anthostrobilus." The earlier form of anthostrobilus (such 

 as occurs in modern Gymnosperms, and in the Mesozoic 

 Benettitea£) is called a pro-anthostrohilus. The h5^o- 

 thetical, direct ancestors of the Angiosperms are called 

 " Hemiangiospermce," and the possible order of evolu- 

 tionary development is conceived by Arber as follows: 



5. AngiospermEe 



Mesozoic and Tertiary (Recent) 

 Eu-anthostrobilata3. 



Mesozoic — ^Pro-anthostrobilatae. 



4. Hemiangiospermse 



(Fossils unknown) 

 3. Cycadofilices 

 2. Heterosporous fern-lilie 



ancestor I Paleozoic — Non-strobilate 



I. Homosporous fern-like I ancestors. 



ancestor J 



148. Ancestors of the Gymnosperms. — ^As far back as 

 Devonian time, preceding the great coal period (Carbon- 

 iferous), fossils have been found of a plant, Cordaites (of 

 the order Cordaitales), common in that period, and 

 having characters which indicate that it stands in the 

 ancestral line of our modern conifers — that it and the 

 conifers had a common ancestry. 



The leaves of Cordaites resembled those of the Kauri 

 pines {Agathis) of the southern hemisphere (Fig. 109), 

 or the leaflets of Zamia. They varied from a decimeter to 

 over a meter in length. The male cones resembled those 

 of the still living Ginkgo, each stamen having from four 



