20 



MAZOCARPON OEDIPTERNUM 



Stele. 



5 mm 



Lam. 



Fig. 3a. — Outline tracing of immature mi- 

 crosporophyll at cone tip. Dark borders in- 

 dicate the extent of subdermal sclerotic tissue 

 and sporophyll trace. Thin-walled tissue 

 stippled. s=subarchesporial pad. From C. B. 

 124 E (27). 



b. — Outline tracing of median section of 

 ripened microsporophyll showing sporangium 

 (Sporang.) still containing microscopes but 



and are also indicated diagrammatically 

 in text figures 3b and 3c inside the 

 dorsal loop (DL). The trace follows 

 along the upper part of the pedicel 

 but does not enter the ridge of tissue 

 which attaches the sporangium, nor does 

 there seem to be any special develop- 

 ment of transfusion tracheids on the 

 ventral side of this portion of the trace 

 (see plate 6, fig. 7) although food must 

 have been actively transferred along 

 this line during sporangial development. 

 Lack of ventral transfusion tracheids 

 in the sporangial attachment is in con- 

 trast to the condition described for 

 Mazocarpon shorense. The traces while 

 still in the cone axis contain a large 

 number of characteristic spiral and an- 

 nular elements such as are shown on 

 plate 6, figure 8. The traces originate 

 from the stele at an acute angle and 

 connect there with exarch spiral and 

 annular protoxylem elements. Plate 6, 

 figure 5, shows an extreme tangential 

 section of a stele which includes one 

 of these protoxylem groups. The stelar 

 metaxylem is made up of somewhat 

 larger scalariform elements as shown in 

 figures 4, 6, 9, and 10 of plate 6. In 

 many specimens the stele contains a 

 pith, composed of prosenchymatous cells 

 (fig. 6). Generally a few isolated trach- 

 eids, apparently annular, are dispersed 

 in the central tissue of these steles 

 (figs. 9 and 10). In some cones the zone 

 of metaxylem. is relatively thick with a 

 corresponding decrease in the amount 

 of medullary tissue (fig. 4), and occa- 

 sionally the pith is absent (fig. 3). The 

 primary protoxylem points seen in cross- 

 sections vary from about 10 to 12. Their 

 arrangement indicates a spiral sequence 

 in some specimens but more commonly a 

 verticillate arrangement (fig. 10). There 

 seems no reason for assuming that the 

 number of protoxylem points is invaria- 

 ble or that the phyllotactic arrangement 

 of sporophylls is inflexible. 



with wall broken (tract.), its attachment to 

 the pedicel (Ped.); the sporophyll trace (Sp. 

 Trace) with its dorsal loop (DL) ; the ligule 

 (Lig.), lamina (Lam.), and dorsal heel (H). 

 From C. B. 124 E (32). 



c. — Outline tracing of median section of 

 ripe sporophyll as given above in &. The lam- 

 ina is slightly longer than usual. From C. B. 

 124 E (27). 



