160 Plant Life and Evolution 



outer set of stamens and the carpels are reduced to 

 two. The outer floral leaves are differentiated into 

 a calyx or outer envelope, and a corolla, the inner 

 highly colored set of floral leaves. 



When we try to determine the relative rank of 

 these two series, we are met by much the same 

 difficulties that we encounter in attempting to trace 

 the connection of the angiosperms as a whole with 

 the gymnosperms or pteridophytes. So far as the 

 geological record goes, the two types seem to have 

 developed almost simultaneously. It was formerly 

 supposed that certain Paleozoic and early Mesozoic 

 impressions of leaves belonged to monocotyledons, 

 and that the greater antiquity of the latter was es- 

 tablished ; but much doubt has been thrown upon the 

 nature of these fossils, and they are now generally 

 considered to be remains either of Cordaitales or 

 cycads. As the great majority of living monocoty- 

 ledons are herbaceous plants, often of very delicate 

 texture, it is by no means unlikely that they may 

 have existed earlier than is indicated by the fossil 

 record, and the same may be said of some of the 

 lower types of dicotyledons, although in the latter 

 group, many of what are regarded as primitive 

 types are trees, like the willow, poplar, and plane, 

 and these are among the earliest fossil angiosperms 

 that we know. 



Fossil Angiosperms. There seems to be no rea- 

 sonable doubt (see Zeiller : " Elements de Paleobo- 

 tanique," 1900) that remains of both monocoty- 



