2J2 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 

 "anthostrobilus." 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 

 Benettiteae) is called a pro-anthostrobilus. The hypo- 

 thetical, direct ancestors of the Angiosperms are called 

 ".Hemiangiospermce," and the possible order of evolu- 

 tionary development is conceived by Arber as follows : 



j Mesozoic and Tertiary (Recent) 

 5. Angiospermas , 



I Eu-anthostrobilatae. 



4. Hemiangiospermae 



. .. f Mesozoic Pro-anthostrobilatae. 



(rossils unknown) J 



3. Cycadofilices 



2. Heterosporous fern-like 1 



ancestor I Paleozoic Non-strobilate 



i. Homosporous fern-like | ancestors. 



ancestor ] 



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 



