88 MR. MIERS ON THE OUTER FLESHY COVERING OF THE SEED 
i i e branched and extended with the 
vors RUM sin ke of the ovule, and thus spread into 
ehe seters but however they may become thus distributed, they must in 
pst eiselaned within their placentary-envelope, and, as above shown, be 
necessarily exterior to the primine. This placentary sheath, first seen as an adnate 
longitudinal band, and afterwards extended in the form of a complete investiture over the 
iue will be found to assume different phases of development : it may, during this 
itid ix expansion, be reduced to a degree of attenuation not thicker than a mere 
skin, and by desiccation of the matters secreted between it and the primine; both may 
become intimately fastened together, as we know occurs frequently with the primine and 
secundine, in which case the ramified bundles of wessels would thus become enclosed 
within this apparently simple, but really compound tunic, pose Whois of _— 
mosing nervures, such as I have figured in the testa of Tovomita and Qommiuhea , and 
by a careful dissection of this sort of tunie, we find the confirmation of this structure. 
In other cases, where the nourishing vessels remain compacted in one simple bundle or 
cord, we may conceive that the placentary sheath, which originally enclosed them, has 
extended itself over the primine in the manner deseribed, and has become developed in 
the form of such an arilliform tunic, as we find in the Clusiee and Magnoliaceæ, the 
raphe in such case necessarily remaining quite free from the testa. Inconsistent in result 
as the two opposite cases just referred to, may at first sight have appeared, it is evident 
from this explication, that both are in perfect harmony with one simple and uniform 
action, varied in effect according to the peculiar circumstances under which the secretory 
productions modify the nature of the developments. 
This extension of the placentary sheath may be either complete as I have described 
it, or only partial: such a partial expansion is known to occur in Turneracee, and the 
circumstances under which it is there developed, offer still further confirmatory proofs of 
the placentary origin of the arilliform expansion in the manner above detailed. St. Hilaire 
in his ‘ Flora Bras. Merid.’ pl. 120, figs. 4 and 5, exhibits the seed of Turnera herman- 
nioides, where the raphe’ proceeds from the hilum, one-third way long its ventral face, 
like a cord: beyond this to the summit, and half way down the dorsal face, it spreads a 
the form of a broad fleshy plate or incomplete tunic. The same development is shown in 
plate 121, fig. 5, where, in the seed of Turnera genistoides, the raphe is seen to extend 
above half way from the hilum, as a cord, whence it expands as far as the summit, in the 
form of two broad auricular plates, nearly the length of the seed, one lobe being seen 
upon each of the lateral faces of the testa, forming, as in the preceding species, a partial 
fleshy envelope. Another instance of the enlargement of the placentary sheath.oceurs In 
Asarum, called. by Gærtner an epiphysumt: Dr. Planchon also describes the seed of 
Asarum Canadenset, as being greatly swollen upon its ventral face, along the line of the 
raphe, by a large glandular mass extending from the base to the apex, and filled with oily 
vesicles, as in the fleshy coating of Magnolia; this he denominates a strophiole, and 
* Linn. Trans. xxi. tab. 26. figs. 22 & 31. os + Geertn. de Fruct. 48. tab. 14. 
1 Mémoire sur les développements des vrais et des faux arilles, p, 34. pl, 2. figs. 10 & 11. 
* 
