588 Benson.—Mazocarpon or the Structural Sigillariostrobus. 
DESCRIPTION OF PLATES XVII-XVIII. 
Illustrating Professor Margaret J. Benson’s paper on Mazocarpon or the Structural Sigillariostrobus . 
(All the figures are micrographs.) 
H. = R. H. C. Collection. 
M. = Manchester ,, 
S. = Dr. Scott’s „ 
a. = archegonium; b. = bract; b.l. = aaaxial groove on distal part of the bract; b.s. = bract 
scar; dl. — distal lamella of the megasporange; s. = spore; s.t. = sporogenous tissue; t. = tapetum ; 
tr. — transfusion tissue ; v.b. — vascular bundle. 
PLATE XVII. 
Fig. 1. Obliquely cut megasporange showing four to five megaspores and the persistent 
parenchyma of wall and subarchesporial pad. M. Cn. R. 758 ; Shore, x 12. 
Fig. 2. Horizontal section of the bract showing the distal part and the narrow keel beneath the 
pedicel of the sporange. H. Cn. 37 ; Dulesgate. x 30. 
Fig. 3. A nearly radial section of a megaspore from the same cone as Fig. 18. The venters of 
two archegonia, a , are clearly shown in the prothallus. The spore-wall shows the characteristic 
dentate apiculi. S. Cn. 1927. x 47. 
Fig. 4. Approximately radial section through a spore with the prothallial tissue well preserved. 
The ring at the base is not an archegonium. H. Cn. 41 ; Dulesgate. x 25. 
Fig. 5. A nearly radial section of a partially abortive megasporange showing only two spores. 
The distal lamella, d.l., looks in section like a rhinoceros tusk. H. Cn. 519, 4; Shore, x 12. 
Fig. 6. Tangentially-cut megasporange on bract near distal end of sporogenous region. The 
internal tissue has perished. The relation of the lateral parts of the sporangial lamella to the wide 
bract is shown. H. Cn. 22 ; Dulesgate. x about 20. 
Fig. 7. A tangential section of an abortive sporange showing the extraordinary development of 
tapetal tissue and a few rounded cells which suggest (?) abortive spores. They are not in tetrads. 
The vascular bundle, v.b., in the pedicel is well shown. H. Cn. 519, 6; Shore, x 22. 
Fig. 8. Tangential section of a megasporange attached to a bract. It is one of a series of five 
sections through the sporange. It shows the vascular bundle, v.b., in the pedicel and the parichnos. 
The character of the pedicel explains the easy detachment of the sporange from the bract. H. Cn. 
518, 7 ; Shore, x 24. 
Fig. 9. Oblique section through the distal end of a sporange cutting a megaspore tangentially. 
The spore shows in this plane a circular sectional area. This section explains the occasionally 
circular form of megaspores in incrustation specimens. S. Cn. 1546 ; Halifax, x 26. 
Fig. 10. A transverse section of the peduncle of a cone shown in Fig. 20 and described in the 
text. II. Cn. 527, 2; Shore, x 13. 
Fig. 11. A high-power photograph of the spore-bearing region and upper wall of a microsporange. 
The spores are grouped in tetrads. H. Cn. 526, 12. x about 100. 
Figs. 12 and 13. The two median members of a series of four tangential sections through 
a microsporange (the fourth or most distal in the series is shown in Text-fig. 3). The relative 
size of sporange and bract is very striking; also the large amount of sterile tissue in the sporange 
and the approximation in Fig. 13 to the construction of trabeculae, as in Isoetes. There is no sharp 
distinction, as in the megasporange, between the subarchesporial tissue and tapetum (cf. Fig. 7). 
H. Cn. 526, 13 and 14; Shore, x 23. 
Fig. 13 a. A part of section 13 showing the details of the tapetum. v.b. indicates the position 
of the vascular bundle. As Fig. 13. 
Fig. 14. An obliquely-cut section of a sporange showing the lamella exactly fitting into the 
concavity of the bract. H. Cn. 35 ; Dulesgate. x 9. 
