Mottier . — The Embryology of some Anomalous Dicotyledons. 457 
Theoretical. 
It now becomes necessary to examine the evidence revealed by 
a study of the embryology of the several anomalous dicotyledons, in order 
to show what light knowledge thus obtained throws upon the question 
of phylogeny of the Angiosperms, and what the relative value of such 
knowledge is as compared with that derived from other sources. 
Any consideration of this subject brings the investigator face to 
face with the ever recurring questions, which have received various answers 
at the hands of the most competent observers : Have the Angiosperms 
been derived from the Gymnosperms or directly from a pteridophytic 
ancestor? Have the two classes of Angiosperms had a common or an 
independent origin ? If monophyletic, which are the more primitive, 
Monocotyledons or Dicotyledons ? 
It must be admitted that many, perhaps the majority of the known 
facts, may be reasonably interpreted in the light of opposing doctrines. 
In fact, this has been done in the several theories that have been advanced 
in the past. No matter what answer may be given to the first of these 
questions, the status of the other two will remain about the same. Some 
observers may prefer to adhere to the older view, that the Angiosperms 
have been derived from the Gymnosperms, with Gnetum as the nearest 
living representative of a transitional condition, yet others will undoubtedly 
be inclined to seek the ancestry of the Angiosperms among the Pterido- 
phytes. The dicotyledonous character of certain Gymnosperms has lost 
much of the importance formerly attached to it in the consideration 
of the origin of the Angiosperms, since it has become known that very 
important similarities in structure have appeared independently in 
different organisms widely separated in phylogeny, and because of the 
incomplete geological evidence in regard to Gnetum . The writer prefers 
to regard the gymnospermous origin of the higher seed plants as less 
probable, and believes that the most important evidence points to 
a pteridophytic ancestry. Now, if we assume that the Angiosperms 
have sprung from the Pteridophytes, we have in Isoetes what may be 
regarded as a transitional condition leading to the Monocotyledons, and 
in Selaginella certain embryological characteristics suggestive of a dicotyle- 
donous nature. Professor Campbell (’91) has shown in his thorough 
and exhaustive study of Isoetes the striking embryological resemblance 
between this genus and certain Monocotyledons, and the facts there set 
forth point strongly to the great antiquity of the monocotyledonous 
ancestors. Whether the evidence will justify the assumption of a separate 
pteridophytic ancestry of the two classes of Angiosperms may be seriously 
questioned, especially if we do not regard the character of the female 
gametophyte and the seed-habit of equal phylogenetic value. The writer 
