578 Benson.—Mazocarpon or the Structural Sigillariostrobus . 
of sporangia to be present even if they were not formed on the same cone. 
No distal erect part of the lamina of the bract was secured. 
Section VII. Abortive and Semi-abortive Sporangia . 
More or less abortive sporangia have been met with. In one block two 
were lying at right angles to each other. One was cut tangentially and 
the other radially (Figs. 5 and 7). 
In the upper part of the transversely-cut cone (H. Cn. 527, 1-9) 
sections pass through cone-scales which are possibly abortive microsporo- 
phylls since only megasporangia occur in the fertile parts- 
In the radial section shown in Fig. 5 the form and length of a normal 
fertile megasporange has been attained, but only two megaspores have gone 
on with their development, though the sporogenous tissue is well defined 
in area. Covering the subarchesporial pad is a palisade to which I have 
referred as c tapetal tissue \ A very unusual condition for a full-sized 
sporange is thus presented to us—a body filled with continuous tissue, 
embedded in which are two irregularly-shaped ‘ spores ’. 
The tangential section of another abortive sporange seen in Fig. 7 
shows a much greater development of the ‘tapetal ’ tissue. It occurs above 
as well as below the sporogenous tissue, and, possibly owing to the arrested 
development of ‘ spores ’, has grown into the sporogenous tissue till it meets 
or abuts on one or two enlarged cells which show no sign of tetrad forma¬ 
tion. It is surprising to see such vigorous growth of the tapetum com¬ 
bined with presumably restricted activity in the sporogenous layer. 
The sections through the upper cone-scales in H. Cn. 537, 8 and 9, are 
interesting because of their form. The vestigial sporange has flattened 
down upon the bract, and thus the cone-scale is convex above and below, 
but is provided with a lamellar margin. The contents appear glandular 
and the vascular bundle takes a median position comparable to that in 
a foliage leaf. Reference will be made to these later (see p. 585). 
SECTION VIII. The Problem of Species . 
Throe species are recognized: Mazocarpon Petty carouse , Mazocarpon 
Shorense } Mazocarpon Cashii. 
Mazocarpon Pettycurense. Two specimens have been secured from 
the Calciferous Sandstone Series of Pettycur, Scotland, and are thus of 
Lower Carboniferous age. These show distinctive characters, although not 
fully know 
More megaspores are seen in a tangential section of the sporange than 
have been seen in any similar section in the Upper Carboniferous forms. 
The microsporange is smaller than the-Upper Carboniferous specimen. It 
is about 4 mm. across, while the latter is 5 mm. across (Figs. 10 and 11). 
There is a layer of small cells beneath the palisade in the Pettycur micro- 
