1 70 Prof. Don's Descri'ptions of two netv Genera of the 



natural to consider the placenta as forming a part only, than that it should 

 constitute the whole of what we regard as the pericarpiuni. 



The circumstance of buds being developed upon leaves is by no means so 

 rare an occurrence as Dr. Schleiden supposes ; for not only Bryophyllum, 

 but Kalanchoe, Rochea, Echeveria, and other genera of Crassulacew, are well 

 known to be readily propagated by their leaves, which give birth to buds, and 

 where care has been taken to cut them off above the point of insertion, so as 

 to avoid the possibility of any portion of the axis adhering to them. The seg- 

 ments of the leaves of Cardamine pratensis and amara separate from the mid- 

 rib in autumn, take root, and give birth to a young plant. In the autumn of 

 1836, while walking round the gardens of the Marquis of Ailesbury at Tot- 

 tenham Park, Wilts, I was much gratified by observing a numi)er of plants of 

 a variety of the common Cabbage {Brasslca oleraceu) having their leaves 

 covered with innumerable buds on the upper surface along the costse and 

 veins. The petiole and lamina of such leaves in other respects presented the 

 ordinary appearance. But the most convincing proof of the origin of ovula 

 from the carpellary leaves is afforded by a singular variety of the common 

 Wallflower {Cheiranthus Cheiri), first observed by Mr. Brown, in which the 

 stamina are converted into open confluent carpels, which bear ovula at their 

 margins *. These facts go clearly to prove the correctness of the opinion which 

 derives the ovula from the carpellary leaves ; and I am disposed to think that 

 the case of the Yew (Taxus), singular as it is, will not be found to be an 

 exception to the general law. I might also notice the female inflorescence 

 of Cycas, which is clearly a modified frond, although I am aware that the 

 mode of evolution of the fronds in that genus might be objected to their being 

 leaves. 



The wood in Cryptomeria is compact, and the fibrous tissue is composed of 

 very slender vessels, united generally by their truncated ends, and furnished 



* Mr. Brown, who has studied with great attention and success the various changes and deviations 

 which take place in the organs of plants, had the kindness to show me a series of beautiful drawings 

 of singularly instructive monstrosities, in some of which one half of the anther was seen to bear 

 ovula at its margin, while the other lobe remained in the ordinary condition, and contained pollen, 

 the filament being entirely unchanged, and showing clearly that no part of the axis was present. — 

 See Linn. Trans, vol. xii. p. 90., and vol. xiii. p. 212, where these drawings are referred to by 

 Mr. Brown. 



