i 
326 BOTANICAL GAZETTE [MAY 
essential features was an angiosperm, in spite of the fact that sev- 
eral modern authorities hold the contrary opinion.’ 
The isolation of the angiosperms, long recognized, has been 
emphasized by recent work. On the one hand, the connection 
of gymnosperms with pteridophytes has been so far traced 
through forms now extinct that the degree of relationship between 
those groups can be estimated, while no link has been found to 
connect the angiosperms with any other group. Thus our igno- 
rance of their genealogy is the more obvious by contrast with 
increasing knowledge concerning that of other vascular plants. © 
On the other hand, the internal structure of the embryo sac both 
before and after fertilization has been shown of late to separate 
angiosperms from other forms even more completely than was 
formerly supposed. 
The gulf which Separates angiosperms from all other plants is 
indeed of unknown depth. By comparison the internal bound- 
ary which divides monocotyledons from dicotyledons is very 
insignificant. The points of resemblance between members of 
these two classes are far more numerous and more important 
than those in which they differ, 
Translated into the language of evolution, this means that the 
angiosperms are a race of considerable antiquity, which at some 
epoch in its history gave rise to two branches, monocotyledons 
and dicotyledons, If this is the case, it is clearly a point of great 
importance to obtain some notion of the structure of the primitive 
angiospermous stock. 
Whatever the primitive angiosperm may have been, we may 
fairly assume that it was not a perfect mean between the mono- 
cotyledon and dicotyledon, nor on the other hand totally unlike 
either. Which did it most resemble? In other words, which 
type is the more primitive? : 
This is no new problem. It has been debated for upwards of 
fifty years, and during that period most botanists have main- 
tained the superior antiquity of monocotyledons. Of late this 
*BaLFour, I.B., Presidential address to section K of the British Association. 
Tgo1, CouLTER, J. M., The phylogeny of angiosperms. Decennial Publ. of University 
of Chicago. 1903. ; 
