248 
CONTRIBUTIONS TO BOTANY. 
— an assumption strengthened by the original observations of 
Brongniart ; but it might possibly be argued that this coating 
is developed from the primine of the ovule, simultaneously with 
the intermediate tunic in which we find the double raphe-like 
cord, in the same manner as has been contended, in the case of 
Magnolia (which I have endeavoured to show has been contested 
upon erroneous grounds), that these two tunics form a compound 
testa, both developed from one single ovular coating, the pri- 
mine. Against this supposition, in the case of Rhamnacete, many 
serious objections present themselves, in addition to those I have 
elsewhere advanced* : — 1. No trace of vessels of any kind is found 
in the outer coating. 2. There is no scar or other mark upon 
the apex of this outer coating, to indicate its previous attach- 
ment to the chalaza of the intermediate raphigerous tunic ; on 
the contrary, there is always a considerable vacant space between 
that summit and the chalaza. 3. In many species of Rhamnus, 
this external crustaceous covering does not form an entire coat- 
ing, but is open from top to bottom, as an enfolded fiat plate 
would be : this could not possibly happen if it were a resilient 
portion of the growth of the primine. 4. In the ovule, we find 
a long funicle supporting it, which disappears altogether in the 
seed. 4. This disappearance of the funicle takes place very 
soon after the period of impregnation of the ovule, when it 
becomes lost within a thickening around the micropylar extre- 
mity of the primine, which is then enclosed by it, apparently as 
if this thickening, and the formation of the outer crust, pro- 
ceeded from an expansion of the funicle. We may hence draw 
the almost certain conclusion that this external seminal tunic is 
of adventitious origin, and of a distinct growth, subsequent to 
the period of the fertilization of the ovule. 
In regard to the yet more external brittle covering of the seed 
of Alphitonia, there appears no sufficient evidence to indicate 
the precise source of its origin with any degree of certainty ; 
but the facts I have already recorded concerning the sterile car- 
pels are of some-value towards this end. It may be argued, as 
indeed it has already been suggested by Dr. Asa Gray {ante, 
p. 246), that this covering may belong to the pericarp, and not 
to the seed. This suggestion, however, may be regarded under 
two distinct points of view : the covering may be considered 
either as consisting of a resilient portion of the endocarp, or 
as a separate development formed within it, analogous to the 
ordinary arilliform productions around seeds. The former view 
conforms with the suggestion of Dr. Asa Gray, and coincides 
with the line of argument adopted by him in regard to the seed- 
* Linn. Trans, xxii. 86 ; Ann. Nat. Hist. 3 ser. i. p. 280 j ibid. ii. p. 185 ; 
ibid. iii. p. 132, note, and pp. 144, 145, note. 
