586 Benson.—Mazocarp on or the Structural Sigillariostrobus. 
seems to have been framed so as to act as the fulcrum when the bract 
above straightens. Each prothallus-would normally secure, by means of its 
toothed wall, a portion of the sterile sporangial (nucellar) tissue when the 
sporange broke up, and thus theoretically we find eight seed-like bodies 
produced from one sporange. Both the type and the adjustments are new 
to botanical literature. 
b. Possible bearing of the facts ascertained on the problem of the Affinity 
of the Pleuromoia and Isoetes , and of genera of Lepidodendreae. 
Throughout the discussion on the incrustation specimens of Sigillario¬ 
strobus, whether by Goldenberg, Zeiller, or Kidston, mention has been made 
of the resemblance the genus Sigillaria shows to Isoetes . 
It may be worth while to inquire whether our new knowledge of the 
structure of the cones we must now attribute to Sigillaria gives us any 
corroboration of this view. 
Potonie summarized 1 the resemblances as respects vegetative organs 
and accepts Pleuromoia as an intermediate form occurring rather happily in 
an intermediate epoch. 
The character in which the sporangia of Isoetes agree with Mazocar port, 
besides the Lepidostroboid characters of radial extension, &c., is the per¬ 
sistence and relative abundance of sterile tissue. Isoetes shows trabeculae 
in both mega- and microsporangia which may be suggestively compared 
with the large trabeculae of the Mazocarpon microsporange (Fig. 13). It 
is possible also that the Mazocarpon type of sporange may afford some clue 
to the better interpretation of the unusual features of the cone of the 
Mesozoic incrustation, Pleuromoia . The wedge-shaped distal part (Text- 
fig. 3) of the Mazocarpon microsporange is not unlike the projecting 
(i. e. distal) part of the sporange in Pleuromoia , as seen in Potonie’s 
Fig. 453 B in the above-mentioned treatise. Moreover, some of the appa¬ 
rent irregularity of the cone of Pleuromoia may be due to the difficulty of 
distinguishing the wedge-like expansion of the sporange from the bract 
which appears similar to it in outline. 
It is even possible that such an expansion may, in an incrustation, have 
adhered to the bract above and thus given rise to an appearance of 
a sporange growing on the lower surface; but the figures given by Solms- 
Laubach 2 are more suggestive of the sporange being partly inserted in 
a fovea, as in Isoetes. In fact the regular striations of the Pleuromoia 
sporangia are more reminiscent of the trabeculae of Isoetes than of the bulky 
irregular trabeculae of Mazocarpon . From these considerations it becomes 
possible to accept freely the suggestion of affinity between the genera if 
judged solely on the characters of their vegetative organs. Prof. Lang's 
1 Engler: Pflanzenfamilien, Teil I, Abt. 4, p. 752. 
2 Solms-Laubach: Bot. Zeit., Heft xii, 1899, p. 227, Fig. 7, Taf. VIIL 
