CONTRIBUTIONS TO BOTANY. 
233 
long furrow, or compressed bilabiate slit, which is always per- 
vious. This outer shell is uniform in thickness, homogeneous in 
texture throughout, and under the microscope is seen to be com- 
posed of numerous narrow, transverse, hyaline cylinders, appa- 
rently solid, of equal size, all placed in a direction radiating from 
the centre of the seed ; so that when the shell is viewed through 
either of its faces, it appears like a reticulation of minute hexa- 
gonal cells, each cell corresponding to the end of a long cylinder : 
by continued maceration, these cylinders may be separated from 
each other ; it is clear, therefore, that in this organization there 
is not the slightest approach to any longitudinal vascular conti- 
nuity. For reasons to be shown presently, we may infer that 
this shell is not one of the ordinary integuments developed from 
any of the original tunics of the ovule, but of posterior growth, 
and therefore not a testa, as hitherto supposed : it is a produc- 
tion apparently analogous in its structure to the outer tunic 
formerly described in the seeds of Cucurbitacece'^ . 
Within this shell, and adhering to it, is a second tunic, which 
is membranaceous, and agglutinated to it by means of a thick 
* Trans. Linn. Soc. xxii. 92 & 108. More extended observations upon 
the seeds of different Cucurbitacea have led me to modify the inference 
made in that stage of the inquiry {loc. cit.), that the more external covering 
(there described as formed of three several portions) consists of epiderm, 
mesoderm, and endoderm — terms incorrectly apphed to parts evidently 
distinct in their origin. The outer very thin stratum of that fleshy cover- 
ing is reticulated with long hexagonoid cells, and its origin may be traced 
to an extension of the outer membrane of the funicle ; the intermediate 
soft substance is a collection of lax fleshy cells intermixed with numerous 
araneiform filaments, all probably emanating from the fleshy substance of 
the funicle. In many genera this fleshy parenchymatous substance is en- 
tirely wanting, so that the shell of the seed is covered simply by the above- 
mentioned thin pellicular membrane. In the centre of the funicle a thick 
cord of vessels is seen, which, as it approaches the seed, is observed to 
bend towards one side, and to enter one of the ends of the linear basal slit 
of the hard tunic ; there is no appearance of its bifurcation at that point, as 
the vessels of the funicle appear to be immediately connected with only- 
one of the two extremities of the peripherical raphe, which meet together 
in the base of that tunic. This hard crustaceous shell, usually called the 
testa, presents no sign of any organic connexion with the two layers of 
structure before mentioned, nor with the more internal tunic. The exist- 
ence of a small thickening or chalazal spot on the summit of the inner 
integument, and of another round its contracted basal neck, is constant 
in all the seeds I have examined. The raphe is invariably peripherical, and 
undisturbed in its course by the apical chalaza, which it crosses : it is also 
free from the shell in all parts, except at its two basal extremities, which 
are both imbedded in channels formed in the crustaceous thickening of the 
shell around its base ; but one of these extremities only, as just said, ap- 
pears to be a eontinuation of the cord of the funicle. The imbedding of 
the two extremities of the raphe in a crustaceous deposit in the base of the 
shell is analogous to the structure observed in many genera of the Rham- 
nace<B. 
VOL. I. 2 H 
