AND PECULIAR FORM OF THE EMBRYO IN THE CLUSIACE.E. 255 



Connected with the issue of this question is that of the origin and mode of growth of 

 the arilliform covering of seeds, which by St. Hilaire is considered to be of two kinds ; 

 one designated by him the true arillus, the other the false arillus ; the former he defines 

 as an envelope open at its extremity, while the latter entirely covers the seed*. This has 

 been well discussed by Dr. Planchon, in an able memoir on the subjectf, where he greatly 

 modifies the views of St. Hilaire, and proposes to give to the false arillus the name of 

 arillode. Under this point of view, both kinds of envelope are alike in colour, texture 

 and form, being either gland-like, lobed, laciniated, more or less cupuliform, or entire and 

 wholly concealing the testa ; their difference consisting in this, that the arillus, whether 

 abbreviated or entire, always covers the micropyle of the testa, while the arillode con- 

 stantly exhibits a minute or larger opening in its surface, around the micropyle, which is 

 never covered by it (loc. cit. p. 10), and he further points out the mode of distinguishing 

 the one from the other. " Si cette ouverture (le micropyle) est cachee par l'enveloppe, ou 

 si elle doit l'etre, dans le cas ou celle-ci serait prolongee, on a un veritable arille. Si le 

 micropyle, au contraire, n'est pas recouvert par l'enveloppe, ou ne peut l'etre meme par 

 cette derniere prolongee, nous aurons un faux arille du meme genre que celui de YEuo- 

 nymus." It will be seen that St. Hilaire points to Euonymus as an instance of his true 

 arillus : Dr. Planchon, on the contrary, selects that genus as offering the type of his 

 arillode. He traces the distinction that exists between them from their different sources 

 of origin, attributing the growth of the true arillus over the ovule to a gradual enlarge- 

 ment of the funiculus, and noticing its earliest appearance from a mere swelling of the 

 umbilical cord to its gradual increment and ultimate development ; but the arillode he 

 states to be derived from an enlargement of the mouth of the exostome or foramen of the 

 ovule, its margin being reflected and produced over the primine, thus growing upon it in 

 the form of an additional tunic. In either case, whether this accessory coating be of the 

 nature of arillus or arillode, it is clear, if it be entire, that the raphe must necessarily be 

 enclosed within it. The arillus, according to this view, is found in the Passifloracece, 

 Dilleniacece, Anonacece, Samydacece, Turneracece, Bixacece, Sapindacece, &c, while the 

 arillode is conspicuous in Celastracece, Cactacece, Malvaceae, Biittneriacece, Euphorbiaceoe, 

 &c. : in this latter family, however, the peculiar carunculoid swelling around the micro- 

 pyle (I do not allude to the fungous strophiole) is called arillode, while that integument 

 which I take to be the true arillus in that Order (note, p. 253) is considered by Dr. Planchon 

 to be a mere epidermis of the testa. It would indeed be difficult to discriminate between 

 a thin arillus and a thick epidermis, as both appear to be of the same nature, differing 

 only in their relative thickness. The origin of the arillus is now well established, but 



ordinarily thick testa for the endocarp of the putamen, and calls the inner integument its testa. I have observed, 

 however, the existence of this cord springing from the point of attachment of the hilum to the base of the cell of the 

 putamen, and extending along one side to the summit of the cell, where it penetrates the very thick testa, to unite 

 with the inner integument at the cotyledonary end of the embryo. The very peculiar nature of this testa, together 

 with the small inferior radicle, and the existence of two large distinct fleshy cotyledons in the embryo, added to other 

 differences in the structure of the flower, and the peculiar venation of its leaves, all serve to remove this genus from 

 the Clusiacea, its position being probably in Lophiriacece, as was long ago suspected by Prof. Lindley. 



* St. Hilaire, PI. Us. no. 43. p. 4. 



f "Memoire sur le developpement et les caracteres des vrais et faux arilles," &c. Montpellier, 1844. 



