176 
CONTRIBUTIONS TO BOTANY. 
beneath the chalaza, there is always a distinct chamber, into 
which the vessels of the raphe find their way ; the third tunic 
is opaque, somewhat membranaceous, with a large orbicular 
chalaza at its base, corresponding with the chalazal base of the 
bony tunic. Xo structure of this kind is seen in the Elceo- 
carpeoe ; but it is constant in all the Tricuspidariece. An ana- 
logous organization is observable in the Sloanece^ the seeds of 
which have a similar red-coloimed fleshy covering, which has 
been designated by some authors an arillus ; the second tunic 
is osseous, and broadly truncated at its base by a large orbi- 
cular chalaza ; but this wants the hollow chamber below it, 
which forms a characteristic feature in the Tricuspidariece. 
In regard to the natiue of these seminal envelopes, the outer 
coat may be regarded as an arilline., analogous to a similar 
tunic which I formerly described covering the osseous coat in 
the seeds of Clusia and Magnolia*. Upon the nature and 
origin of these integuments I then endeavoured to offer an ex- 
planation, which was contested by others, who maintained 
that in these cases the outer fleshy covering is merely the epi- 
dermis of the bony coat, both being elicited by the growth of 
one single tunic, the primine of the ovule. There is a bar to 
such an argument, in the instance of Ardstotelia, in the ex- 
istence of the singular appendage upon the outer fleshy coat, 
resulting from the duplicature of that integument, which could 
not occur if it were merely an epidennis. By those who have 
not studied the subject, the origin of this appendage might be 
attributed to a fungous enlargement of the funicle (as Gaertner 
supposed in an analogous instance f) or to an expansion of the. 
chalaza ; but a more careful examination will show that it 
is too remote from the latter and from the hilum' to admit 
of such a supposition. Whatever be its origin, this outer tunic 
appears to be an integument wholly independent of the bony 
siiell, consisting of its reticulated epiderm, a fleshy mesoderm 
replete with resinous cells, and an endoderm in the form of a 
white, opaque, reticulated cuticle, separable from the shell, 
the chord of the raphe being foimd within its substance. 
The fact that this fleshy tunic and bony shell are two dis- 
tinct integuments is shown by an examination of the unim- 
pregnated ovules in the abortive cells of Aristotelia : here, 
with the ovules grown to the length of half a line, I have 
succeeded, by means of a longitudinal section, in actually sepa- 
rating them. The tunics, which, if fertilized, would have 
grown into the fleshy coating and bony shell, are then seen as 
two distinct, thin, membranaceous integuments, easily separa- 
* Linn. Trans, xxii. 89, tab. 19. figs. -56-59; Contrib. Bot. i. 219; Ann. 
Nat. Hist. ser. 3. i. p. 276. t De Fruct. ii. 271. 
