284 MORPHOLOGY OF ANGIOSPERMS 



acters, but still more from the nature of the embryo and the 

 structure of the stem, that the primitive Angiosperm stock 

 would be the Dicotyledons. Strasburger recognized this neces- 

 sity when proposing the theory, and regarded the Monocotyle- 

 dons as a reduced branch from the Dicotyledons ; which is 

 another reenforcement of the argument derived from recent 

 anatomical investigations. In fact, the Gymnosperm ances- 

 try of Dicotyledons also gains a point in the entire absence 

 of pteridophytic anatomical features in the shoots of Dico- 

 tyledons. 



Lately, also, Karsten, 16 in a morphological study of the 

 Juglandaceae, emphasizes their resemblances to Gymnosperms, 

 and concludes that the Angiosperms have been derived from such 

 forms as Gnetum. The historical argument against such a claim 

 is the absence of any certain evidence of the existence of Gnetum 

 among the numerous Angiosperms of the Cretaceous and Terti- 

 ary. If it were related in any way to the origin of such a group as 

 the Angiosperms, it seems probable that it would have left some 

 evidence of its existence. Of course this is negative evidence, 

 and remains of ancient Gnetales may be found in the tropics 

 or in the southern hemisphere. The argument from the pres- 

 ence of a perianth is particularly vulnerable, since the so-called 

 perianth merely represents the bracts common among Gymno- 

 sperms, and the most primitive Dicotyledons and Monocotyle- 

 dons have no perianth. Further, the presence of true vessels 

 is an argument as much in favor of the origin of the Angio- 

 sperms from certain heterosporous Pteridophytes as from Gne- 

 tum. Although we regard the origin of Angiosperms from 

 Gymnosperms as very improbable, the embryo-sac structures 

 of Gnetum are suggestive of the way in which the character- 

 istic sac-structures of the Angiosperms may have arisen from 

 a compact gametophyte. This is all the more probable since 

 the sac-structures of certain Juglandaceae and of Peperomia 

 pellucida have been found to be suggestive of those of certain 

 species of Gnetum. 



If the Gymnosperms are not the ancestral forms of the An- 

 giosperms, their direct derivation from the Pteridophytes be- 

 comes a matter of course. The Pteridophyte that has been most 

 persistently associated with the origin of Angiosperms is Isoe- 

 tes. Its resemblances to the Monocotyledons have suggested 



