88 MR. MIERS ON THE OUTER FLESHY COVERING OF THE SEED 



sini^le cord, or a portion of them in excess may become branched and extended with the 

 H'rowth of the placentary sheath over the whole surface of the ovule, and thus spread into 

 numerous ramifications ; but however they may become thus distributed, they must in 

 all cases remain enclosed 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 

 primine, will be found to assume different phases of development : it may, during this 

 subsequent 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 bimdles of vessels would thus become enclosed 

 ■\ntliin this apparently simple, but really compound tunic, presenting a series of anasto- 

 mosing nervures, such as I have figured in the testa of Tovomita and Commirhea*, and 

 by a careful dissection of this sort of tunic, 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 described, and has become developed in 

 the form of such an arilliform tunic, as we find in the Cliisiece and MagnoUacece, 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 tliis 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. 



Tliis 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 Turner acece, 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. HUaire 

 in his ' Flora Bras. Merid.' pi. 120, figs. 4 and 5, exhibits the seed of Turnera herman- 

 nioides, where the raphe proceeds from the hikmi, one-thu'd way long its ventral face, 

 like a cord : beyond this to the summit, and half way down the dorsal face, it spreads in 

 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 hUum, 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 occurs in 

 Asarum, called by Gsertner an epiphysumf : Dr. Planchon also describes the seed of 

 Asarum CanadenseX, 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. \ Gsrtn. de Fruct. 48. tab. 14. 



X Memoire sur les ddveloppements des vrais et des faux arilles, p. 34. pi. 2. figs. 10 & 11. 



