OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
501 
bract shows it to be, as is also the case in the Burntisland species, an extension of the 
epidermal layer of the bract. But in this new species I find what I have not previously 
observed in these sporangia : an apparently distinct inner membrane, c, investing the 
mass of microspores. The inferior keel, d, of the bract is also much shorter than the 
elongated one of the Burntisland plant. The entire maximum diameter of the sporan¬ 
gium, including its bract, is only '05, corresponding in this respect with the proportions 
of the crushed strobilus, fig. 8. 
The relations between the structure of these primeval spores and sporangia and that 
of recent ones are not devoid of interest. In my last memoir I showed that each 
macrospore consisted of a very thick dark-coloured outer layer, and a very thin inner 
one. I think I cannot err in regarding the former as the representative of the exos- 
poriurn and the latter as the endosporiiun of the spores of living Lycopods. The 
macrospore of the recent Selaginellci Martensii possesses a similar thick dark-brown 
exosporium. I have already identified the cells contained within the endosporiiun of 
the fossil species with the endospermic cells of the recent ones. I have searched, but 
thus far in vain, for any representative of the prothallus which many living macro¬ 
spore develop in addition to the endospore. The structure of the sporangium also 
requires to be observed. In most living Lycopods the sporangium-wall possesses, in 
its early state, three distinct cellular layers—an outermost epidermal one, which is 
merely the uplifted epiderm of the parent plant, and two subjacent layers of chloro¬ 
phyll-bearing cells. As I have already explained, the wall of the fossil sporangium, 
fig. 10, consists of two layers. The outer one, b, is obviously identical with the epi¬ 
dermal layer of living forms. This is made clear equally by its structure and by the 
way in which it terminates interiorly on the surface of the bract, a. The inner mem¬ 
brane, c, appears to be structureless ; but when we remember that in recent sporangia 
the three layers eventually become reduced to two as the spores ripen, through 
changes that affect the two inner or chlorophyll-bearing layers solely, I shall probably 
not be far wrong in regarding the layer, fig. 10, c, as the representative of these 
layers. 
In Plate 22, figs. 38-57, of memoir IX. I gave representations of a new strobilus 
with spores of one kind and of a peculiar character ; but in the only specimens of that 
strobilus which I then possessed the structure of the central vascular axis of this fruit 
was very imperfectly represented by a crushed mass of vessels. I have more recently 
received from Mr. Spencer, of Halifax, transverse sections of a second specimen of 
this strobilus, in which the central structures of the axis are well preserved. The 
outer bark (fig. 11, d) in these sections corresponds with that of fig. 53, b, of the pre¬ 
vious memoir, except that the cells of its inner portion (fig. 11, d') are more delicate, in 
comparison with the outermost ones, than in the older specimen; the bracts (fig. 11, e ), 
also composed of numerous much-elongated cells, are longer and do not exhibit any 
proof of their having been so much expanded at their free extremities in a lateral 
direction as fig. 56 of the previous memoir showed them to have been vertically. In 
MDCCCLXXX. 3 T 
