Mr Carpenter on Unity of Function 



is sufficiently obvious. I may, however, point out the corres- 

 pondence both in structure and function, between the cotyle- 

 dons* of plants, especially such as are membranous) and the 

 temporary branchiae, which, as is now well known, may be 

 traced in the embryos of all the higher animals. 



That the embryo of -flowering plants takes its origin in a 

 simple vesicle, analogous to that which forms the entire germ 

 of the cryptogamia, is now well understood ; indeed, I think it 

 would be easy to apply in detail to vegetables the doctrines of 

 *' fundamental unity of structure," which Dr Barry has shewn 

 from the researches of German embryologists to exist through- 

 out the animal kingdom, and which he has spoken of as appli- 

 cable to organised beings in general .+ One speculation I may 

 hazard at the present time, leaving it to abler botanists to de- 

 ci'de upon its merits. The embryo of flowering plants continues 

 to be developed during the ripening of the seed, so that at the 

 period of maturity the cotyledons are fully formed, and the 

 plumula and radicle are ready to elongate themselves into an 

 ascending and descending axis. The spore of a cellular plant, 

 on the other hand, being a simple cell, first produces others si- 

 milar to itself, and these gradually form a leaf-like expansion, 

 such as Mirbel has beautifully shewn in the marchantia, and 

 such as exists at a certain pei'iod in the germination of ferns 

 also.j This leafy expansion it is from which the stem, roots, 

 and o-yrate fronds of the latter class originate ; and when these 

 are fully formed, it decays away. Although the mode of the 

 development of the stem seems in j\Ir Dickie's view to pi'event 

 us from regarding this leafy expansion as a cotyledon, I scarcely 

 see how we can regard it in any other light ; since, physiolo- 

 o-ically speaking, it differs only in this, that the embryo of the 

 fern forms it whilst maintaining an independent existence, and 

 the embryo of the flowering plant whilst supplied with nutri- 



• "Where the cotyledons axe fleshy, that is, contain a store of albumen with- 

 in themselves, they evidently supply also the purpose of the yolk-bag in the 

 ova of animals. 



+ I think it due to myselfj however, to state, that, as far as regards the ve- 

 getable kingdom, these views were previously entertained and expressed by 

 ip.e, although Dr B. was, I doubt not, unaware of the fact. 



X 3Iagazuie of Zoology and Botany, vol. i. 



