and on the Structure of the Seed in the Rhamnacese. 83 



outer crustaceous covering ; and upon this diaphragm is observed 

 the thick cord described by botanists as the dorsal raphe, which 

 rises from the base, crosses the disk-like areole in the summit, 

 and runs down the opposite side of the seed, forming the line 

 first described as seen on the ventral face. The whole of this 

 intermediate integument, with its entire raphe, may be exposed 

 to view if we chip away in small fragments the outer crustaceous 

 coating with the point of a knife, when the two cords, both ven- 

 tral and dorsal, are distinctly seen ; the two teguments are closely 

 adpressed upon each other, except over the ventral cord, where 

 there is always a considerable interval between them, thus show- 

 ing that the raphe has no connexion whatever with the outer 

 crustaceous coating. Beneath the second envelope is a third 

 integument, which immediately invests the albumen, and which 

 is thin and membranaceous ; these two integuments, though 

 free, are in immediate contiguity at all parts of their surface, 

 except along the middle of the dorsal face, where they become 

 separated to form the square hollow channel in the axis above- 

 mentioned, one side of which square, with the imbedded raphe, 

 is formed by the induplicature of the intermediate integument. 

 The embryo is broad and foliaceous, and is covered by a layer 

 of fleshy albumen, equal in thickness to the cotyledons, the 

 margins of the whole, together with the enveloping tunics, being 

 con duplicated into the hippocrepical form at first described. 

 We see here, therefore, the existence of three seminal envelopes, 

 very similar in their nature to those described in Colletia, with 

 this remarkable difference, that in the latter the crustaceous 

 coating is entire, while in Rhamnus it is always incomplete upon 

 one side. In Rhamnus catharticus the groove formed by the 

 conduplication of the seed is generally in the middle of the 

 dorsal face, though sometimes nearly lateral, caused by unequal 

 growth, in consequence of the partial abortion of one of the 

 carpels ; but in all these cases, the two lines of raphe always 

 correspond with the middle of the cotyledons, while in the Col- 

 letiea they constantly run along their margins*. 



The same structure exists in Rhamnus Alaternus; but on ac- 

 count of the small size of its seeds, and the greater tenuity of 

 the several integuments, it requires much care to dissect the 

 parts. The crustaceous covering is very thin, and adheres more 

 firmly to the extremely delicate intermediate integument, and it 

 is therefore difficult to separate them without lacerating the 

 latter ; but when the separation is made with care, we find the 

 ventral portion of the cord imbedded like a white line in that 

 distinct integument, and running from the apex to the base : 



* Analytical details of this structure in Rhamnus catharticus will be 

 shown in plate 33 A of the ' Contributions to Botany. 



