. AND PECULIAR FORM OF THE EMBRYO IN THE CLUSIACEA. 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 {rue 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 subjectt, 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 cachée par l'enveloppe, ou 
si elle doit l'étre, dans le cas où celle-ci serait prolongée, on a un véritable arille. Si le 
micropyle, au contraire, n'est pas recouvert par l'enveloppe, ou ne peut l'étre méme par 
cette dernière prolongée, nous aurons un faux arille du méme genre que celui de |’ Euo- 
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 tunie. 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 Passifloracee, 
Dilleniacee, Anonacee, Samydacee, Turneracee, Bixacee, Sapindacee, &e., while the 
arillode is conspicuous in Celastraceæ, Cactacee, Malvacee, Büttneriacee, Euphorbiacee, 
&e.: 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 
ocarp i i i “I have observed 
inari i f the putamen, and calls the inner integument its testa. F- 
vanis eer : à attachment of the hilum to the base of the cell of the 
however, the existence of this cord springing from the point of i 
utamen, and extending along one side to the summit of the cell, where it penetrates the very thick testa, to unite 
: 1 The very peculiar nature of this testa, together 
: : à | of the embryo. 
with the inner integument at the cotyledonary end of the embry cotyledons in the embryo, added to other 
i inferi i d the existence of two large distinct fleshy 
EM m culiar venation of its leaves, all serve to remove this genus from 
differences in the structure of the flower, and the pe : 
| i iri . Lindley. 
the Clusiaceæ, its position being probably in Lophiriaceæ, as was long ago suspected by Prof. Lindley 
* St. Hilaire, Pl. Us. no. 43. p. 4. en 
+ “Mémoire sur le développement et les caractères des vrais et faux arilles," &e. Montpellier, 1844. 
