826 REPORT— 1901. 



hypothesis that the Monocotyledones are derived from the Dicotyledones ; for 

 here alone, since the dicotylous character of forma like the Dioscorese was shown 

 to be untenable, was there a structure which could be interpreted as evidence of 

 a reduced second cotyledon. The idea that the epiblast is such a structure was 

 enunciated by Poiteau at the beginninfj of the last century, and along with 

 hypotheses of the nature of the other parts of the grass-embryo has been a subject 

 of vigorous discussion since that time. The controversy is not yet closed. Whilst 

 we have Van Tieghem now adopting the view of the cotylar nature of the epi- 

 blast and using it as a character of fundamental taxonomic importance, we liave 

 others who as strongly uphold the interpretation of it, first formulated by 

 Gaertner, as a winged appendage of the scutellum, which is considered to be the 

 cotylar lamella. And, again, there are those who take the view that it is a mere 

 outgrowth of the hypococylar body of the embryo and without any cotylar 

 homology. Our interpretation of the part must depend primarily upon the stand- 

 point from which we view the embryo of Angiosperms. This I shall discuss 

 presently. All I need say here, Apropos of the class of Liorhizal Dicotyledones, is 

 that whatever the epiblast be — and for my part I am disposed to regard this 

 simple cellular structure as merely an outgrowth with a water-function from the 

 embryonal corm — a dispassionate consideration must lead us to hold that it is a 

 bold step to use a character the morphological value of which can be so variously 

 interpreted as one of primary importance for separation of a group of Angiosperms. 

 Moreover, we must remember that the feature of the epiblast is not one of uni- 

 versal occurrence in the Graminese. If we take a well-defined tribe like the 

 Hordeas, as framed by Bentham and Hooker, we find that of eight of its twelve 

 genera which have been examined for this feature five have the epiblast and three 

 want it. And surely the fact of its presence in Triticum and absence in Secale, 

 its presence in Elymus and absence in Hordeum, is strong evidence that the 

 epiblast is not a character of such importance as it would have were it a reduced 

 cotyledon as is asserted. 



It appears to me, therefore, that this third class of Angiosperms has no sound 

 foundation, no more, perhaps less, than Dictyogens and Rhizogens which appeared 

 as parallel groups with Endogens and Exogens in Lindley's old classification. 

 Our present knowledge allows the recognition of only two classes of the angio- 

 spermous type— the Dicotyledones and the Monocotyledones. 



Of Dicotyledo')ies and Monocotyledones. 



The relationship of these two groups is involved in the origin of the angio- 

 spermous type. They may have had a common origin or they may have arisen 

 separately ; and if the former the Dicotyledones may have been a subsequent 

 offshoot froni the Monocotyledones, or the reverse may' have been the case. Each 

 of these possibilities has its supporters. Were I to maintain an opinion it would 

 be that the two classes have arisen on separate lines of descent. The embryo- 

 characters, as well as those of the epicotyl, can, I think, be shown to be funda- 

 mentally different and to alford no basis for an assumed phyletic connection. The 

 difference between Hepaticre and Musci, to take a parallel case in a lower grade, 

 are not more conspicuous. The parallel sequence in development in the two 

 classes are no more than one would expect, and may be regarded as homoplastic. 

 To the question which group is the older I would answer that the Dicotyledones 

 are by far the most adaptive and progressive if — as is not necessarily the case — 

 this can be taken as evidence of their more recent origin. This, however, is not 

 the matter I intend to discuss here. I wish rather to inquire if there are any 

 features broadly characterising the groups to which, as in the case of Angiosperms 

 as a whole, we may look for help to an explanation of the predominance 

 at this time of the type of Dicotyledones. I think there are, but they are 

 not to be found in the reproductive system. That is constructed on suffi- 

 ciently similar lines in each class. The features I refer to are to be found in 

 the construction of the vegetative system both in the embryo and in the adult. 

 That of the former gives the dicotylous plant an advantage in its start on life ; 



