174 APPENDIX. 
7. Hyoscyamee.—This forms a very natural tribe, remarkable 
for the very singular epigynous gland, hitherto I believe new in. 
the history of vegetable physiology, the origin and nature of 
which it is desirable to ascertain. It cannot bear any analogy 
with the true disc, which is always hypogynous in the superior 
ovarium and epigynous in the inferior germen, and which is ge- 
nerally admitted, by botanists to be little more than a confluent 
whorl of abortive stamens. In Cacabus it assumes the form of 
an enlargement of the base of the style, but that it exists here as 
a distinct organ is proved by the swelling seen within the matured 
fruit, in the summit of the cavity of the cells. In Thinogeton it is 
considerably larger, where it appears as a coriaceous thickening 
of the chartaceous covering that forms the upper portion of its 
dry berry. It is however most distinctly developed in Hyoscya- 
mus, even in the young ovarium, in the form of a fleshy external 
gland, which covers more than the superior moiety of the entire 
germen, and on making a longitudinal section it is seen di- 
stinctly adnate upon the true endocarpium : it forms therefore a 
very good discriminating character of this tribe. The cause of the 
opercular dehiscence of the fruit in Hyoscyamus is thus readily 
accounted for, because while the lower half of the pericarpial 
covering remains thin and membranaceous, the opercular portion 
becomes hard and coriaceous, from the indurescence of the glan- 
dular covering above-mentioned *. I have placed doubtfully in 
: dl 
* Although in the above case it is easy to trace the cause of the opercular 
dehiscence of the fruit, the same is not so readily accounted for in other cases ; 
in Anagallis for example. In this last-mentioned instance, a distinct zonal 
line may be seen in the thin pericarpial covering before the ripening of the 
fruit, and it is along this that the membranaceous capsule afterwards bursts, 
by a clean circumscissure. This zonal line however bears no relation to the 
longitudinal true nervures, which may be distinctly traced in the pericarpial 
covering, and which, extending from the style to the base, may be referred 
to the midribs and marginal junctions of the original carpellary leaves: but 
what is the nature of the line which traverses these nervures at right angles 
across all the carpellary Jeaves? This is difficult to be accounted for, unless 
we imagine it to arise from a cause somewhat analogous to the case of Hyo- 
scyamus, only that instead of the line being the marginal limit of an epigy- 
nous gland, it may be the edge of an original elementary hypogynous disc, 
which by its subsequent — and attenuation becomes hardly distin- 
guishable from the rest of the SNe ea On examining this pericarpial 
covering, about the period of the fall of the corolla, this zonal line is seen 
more transparent than the rest of its substance, and not opake, as is ob- 
servable in the regular longitudinal nervures which may then be readily 
traced ; at this period however, and even in the younger state of the ova- 
rium, before this zonal line becomes distinguishable, the lower: half of the 
pericarpial membrane is decidedly of a more greenish hue than the upper 
moiety. This appears to me the only theory on which we can account for 
the dehiscence of the capsule in Anagallis, but in suggesting it, I confess 
that I could not discern the fact of the original existence and ultimate at- 
tenuation of such a disc as I have imagined. Although, generally speaking, 
