170 Prof. Dow's Descriptions of two new 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 pericarpium. 
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, T was much gratified by observing a number of plants of 
a variety of the common Cabbage (Brassica oleracea) having their leaves 
covered with innumerable buds on the upper surface along the costæ 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, 
