Benson.—Mazocarpon or the Structural Sigillariostrobits. 573 
extraordinarily well preserved (Fig. 4). The venters of the archegonia are 
to be seen beneath the scar in a large number of cases (Figs, 3 and 18). 
When the sporange breaks up the ‘ spore * apex invariably comes away 
from the pad, but the base of the 1 spore ’ more frequently retains its con¬ 
nexion with the outer tissue of the sporange (see Fig. 9), a fact which may 
have been of biological advantage, as is the association of the embryo sac 
with the perisperm or nucellar tissue in the more typical ‘ seed \ 
The spore-wall is obviously not rigid throughout development. Its 
base is covered with pointed processes which undoubtedly helped it to 
Text-fig. 2. A diagram constructed from two successive nearly horizontal sections through 
a megasporange on a bract (the keel of the bract is not shown in the section, as it appears in the 
third section of the series). The spores marked with + were cut in the middle section, and one has 
been slightly displaced by a stigmarian rootlet entering the sporange in the direction indicated by 
the arrow. H. Cn. 525, 2 and 3. 
retain its hold on the surrounding tissue. When the prothallus has attained 
its maximum size the wall appears to have become rigid, as there are several 
cases of the prothallial tissue being separated from the spore-wall by 
shrinkage (Fig. 4). 1 
Owing to the permanent tissue uniting the pad to the pedicel of the 
sporange more spores occur in the upper than in the lower horizontal 
plane of the sporange. In Text-fig. 2 five spores are cut in the uppermost 
section (H. Cn. 525, 3), but only three in the lower (H. Cn. 525, 2). The 
latter three spores are marked with + in the text-figqre. As the two 
planes of section were respectively near the upper and the lower surfaces of 
the sporange not a single ‘ spore * has been cut through its organic apex, so 
1 See also Scott’s Studies, Fig. 78, p. 188, 
P p 2 
