OF THE FOSSIL PLANTS OF THE COAL-MEASTTEES. 
241 
that structure, and in close contact with it, the firm membrane (fig. 76,/*) described by 
Dr. Hooker. In its lower or chalazal half this membrane is much more dense than at 
the opposite end of the seed. In the former part it consists of a thin, almost structure- 
less membrane, thickened by the addition of the numerous reticulated cells, already 
described by Dr. Hooker, and derived from the innermost portion of the hard endotesta ; 
but near the middle of the seed, not only do these cells disappear from the membrane, 
but the latter now splits into two layers — an inner one (/') which closely invests the 
perisperm, and an outer one (f") which lines the endotesta, the subdivided membranes 
thus leaving a dome-shaped cavity between them. Fig. 76 is a diagram representing 
this arrangement, but exaggerating the distances beween the several tissues *. At all 
events the position of the cavity corresponds closely with that of my lagenostome, whether 
viewed in its relation to the nucleus or to its investing membranes. 
When making a few observations on these seeds at the Bristol Meeting of the British 
Association in 1875, I proposed for a second seed the generic name of Physostoma \ 
but since my only specimen of it does not exhibit its outer layer it may be better to 
unite it generically with the last species under the name of Lagenostoma physoides. 
Having found but a single example of this very distinct seed I have only been able to 
study it under the two aspects represented in figs. 77 & 78. The former of these is a 
longitudinal section made nearly through the centre of the seed, and the latter is one 
made in the same vertical plane, but nearer to the periphery of the seed. 
* Throughout this memoir I have employed the two terms perisjpermic and nucular to designate the two 
membranes usually found within the testa of these seeds. I have done so for the purpose of making my 
nomenclature harmonize with that of the late H. Broxgniart’s memoir on similar Carboniferous seeds from 
St. Etienne. At the same time I may point out not only the extreme difficulty of identifying these membranes 
with those of the seeds of living Cycads and Conifers, but also the objections which British botanists may 
reasonably entertain to the nomenclature employed. On the former point we must remember that during the 
long protracted development of the ovules of the varied members of the Cycadean and Coniferous families the 
equivalents of the spermoderm and embryo-sac undergo very important changes, rendering the exact compa- 
rison of the recent and fossil forms very difficult. The second difficulty referred to is equally important. 
British botanists apply the two terms perisperm and endosperm very definitely : viz. the former to the tissues 
of the nucleus, and the latter to the contents of the embryo-sac. The nomenclature of M. Broxghtart has not 
recognized this distinction. He speaks of the “sac perispermique, dans laquelle devrait se trouver l’embryon.” 
“ Malgre 1’a.lteration des ces parties interieures, on peut y reconnaitre presque toujours deux enveloppes mem- 
braneuses ; Tune, plus externe, nait au pourtour du chalaze ou sur sa surface superieure, et se termine supe- 
rieurement par une extremite conique qui correspond a l’orifice du micropyle du testa, mais qui en est souvent 
assez eloignee : c’est la surface du nucelle ; l’autre, beaucoup plus alteree, libre et flottante au-dessus de la 
chalaze et se terminant a quelque distance au-dessous de l’extremite conique de la precedente, correspond a 
l’enveloppe du perisperme.” 
These definitions make it clear that the “ perisperme ” of M. Broxgniart is the endosperm of British botanists, 
whilst his “ membrane perispermique ” is the true primary embryo-sac. His “ membrane nucellaire,” on the 
other hand, is the spermoderm of other writers. With this explanation of the sense in which I employ 
M. Broxgxiart’s terms, I can continue to use them in order to avoid confusion on comparing his descriptions of 
the St.-Etienne seeds with mine. At the same time a different use of these terms would have been preferable. 
—July 19, 1877. 
