R. C. McLean. 
308 
however, there lias been no collapse of the megaspore, and in con¬ 
sequence, not only is the gametophyte tissue itself preserved, but 
the nucellus and the vascular bundles retain their true relations to 
the testa, that is to say they are closely adherent to the hypoderm. 
The exact number of vascular bundles present is difficult to deter¬ 
mine, for the reason that, in spite of the excellent preservation of 
some of the structures in the seed, the bundles themselves are com¬ 
pletely rotted away. Judging by the cavities left, the normal 
number of bundles, nine, seems to have been present. 
The nucellus, as mentioned above, is closely adpressed to the 
inner surface of the integument, and is very shrivelled. Within 
this, comes a noticeably thick membrane, which shows a granular, 
and imperfectly preserved appearance. The existing appearance 
of this membrane is not altogether that of a structure originally 
simple and truly membranaceous. 
I owe to Professor Oliver the suggestion that on the analogy 
of the similar structure in Physostoma, this supposed megaspore- 
membrane may really represent the remains of a perished tapetum. 
This is, of course, only a suggestion, and in the present paper the 
previous appelation of “ megaspore-membrane ” is provisionally 
retained. 
The actual prothallus is entirely isolated from this membrane. 
It is incomplete in circumference, about two-thirds of the original 
circular outline being preserved. At one point it has been violently 
separated from the megaspore wall, and a few cell-walls remain 
adherent to the latter. The component cells are naturally very 
thin-walled, but they have been preserved without much shrinkage, 
although the tissue of the prothallus is ruptured in several places, 
leaving large lacunae. Of contents, there are numerous traces, 
the most notable being a faint reticulum which occupies some of 
the cells, and certain opaque granules apparently suspended by 
filaments in the interior of many of the peripheral cells, both of 
which appearances are shown in Plate V (lower figure). 
The entire section is shown in Plate V. The dimensions of 
the principal elements are as follows: 
Entire Diameter of Seed - - 3‘9 mm. 
Average Thickness of Testa - - *2 mm. 
Dimensions of Alveoli Length *07—T3 mm. 
Breadth (average) -03 mm. 
The arrangement of the alveoli in the tissue exhibits features of 
interest. Round the periphery of the prothallus is developed a 
