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 OF .CENTRAL AFRICA. 2G3

seem to imply that in the embryo of this family the posi- tion of the radicle is varia])le, and that of the cotyledons fixed. It is at least deserving of notice that the reverse of this is the fact ; thongli it is certainly not necessary to change these terms, Avhich are now generally received.

On the snbject of Savignya, two questions naturally pre- sent themselves. In the first place — Is this genus, solely on account of its conduplicate cotyledons, to be removed from AlyssinciT, where it has hitherto been })laced, to Vellea), its affinity with which has never been suspected, and to whose genera it bears very little external resemblance ? Secondly — In dividing Crucifera3 into natural sections, are we, with ^[. 13e Candolle, to expect in each of these subdivisions an absolute uniformity in the state of the cotyledons ? As far as relates to the accumbent and flatly incumbent states, at least, I have no hesitation in answering the latter ques- tion in the negative ; and I believe that in one case, namely, Hutchinsia, these modifications are not even of generic im- portance, for it will hardly be proposed to separate H. alpina from petraea, solely on that ground. I carried this opinion further than I am at present disposed to do^ in the second edition of Mr. Aiton's 'liortus Kewensis,' where I united in the genus Cakile plants, which I then knew to differ from each other, in having accumbent and condupli- cate cotyledons ; and I included Capsella bursa-pastoris in the gemis Thlaspi, although I was aware, both from my own observations and from Schkuhr's excellent figure,^ that its cotyledons were incumbent. I am at present, i^u however, inclined to adopt the subdivision of both these genera, as ])roposed by several authors and received by M. De Candolle ; but to this subdivision the author of the ' Systema Naturale ' must have been determined on other grounds than those referred to ; for in these four genera, in which the three principal modifications of cotyledons occur, he has taken their uniformity for granted.

As to the place of Savignya in the natui'al family, I be- lieve, on considering the whole of its structure and habit, that it ought to be removed from Alyssinca? to a subdivision

^ HandO.^ad. ISO.

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