16 



MAZOCARPON OEDIPTEBNUM 



persistent internal tissue and lack of 

 lateral sporangial keels. Microsporangia 

 about 2-2.8 mm. wide, about 4 mm. long 

 and 2.5 mm. high. No intra-sporangial 

 tissue is present in the mature micro- 

 sporangium such as that present in the 

 megasporangium ; the prismatic wall 

 layer is less rigid and more or less casual 

 distortions often occur. In dehiscence 

 a fracture occurs about halfway up on 

 either side of the sporangium and ex- 

 tends over the top at the distal end. 

 This line of fracture is equivalent in 

 position to the slight concavity above 

 the lateral keels of the megasporangia. 

 Usually, the microsporangium is also 

 broken from the pedicel ; sometimes this 

 causes another split at the bottom of 

 the sporangium, and sometimes the 

 spoon-like lower half of the microspo- 

 rangium remains unbroken. The only 

 trace of sterile tissue within the mature 

 sporangium is a thin, somewhat varia- 

 ble, but often ''T" shaped process at- 

 tached radially part way along the pedi- 

 cel. Immature microsporangia at the 

 cone tip show that this is derived from 

 the collapsed tissue of the subarchespor- 

 ial pad. Spores are about 60 /x in di- 

 ameter, slightly triangular, trilete, with 

 rays extending to the equator. Exospore 

 covered with numerous low papillae; 

 endospore smooth and thin. At the point 

 of each of the three pyramic segments 

 of the endospore is a characteristic 

 apical prominence. No endosporal male 

 gametophyte has been observed. 



Co-types of forma microphorum are 

 the two cones illustrated in plate 5, 

 figures 1 and 3 from coal-ball 124 in the 

 Illinois Geological Survey collections. 



MORPHOLOGIC FEATURES 



Plates 1 and 2 illustrate the general 

 features of forma megalophorum. Fig- 

 ures 1 and 2 of plate 1, and figure 2 of 

 plate 2 represent parts of approximately 

 radial sections of a fine cone. The three 

 complete sporangia a, h, c, shown at the 

 left in figure 1, plate 1, vary considera- 

 bly. The upper sporangium a is cut 

 radially but slightly to one side of the 

 center so that the sporangial attachment 

 to the pedicel is missed. Four mega- 

 spores are shown in characteristic ar- 

 rangement. The lower sporangium h is 



also cut radially but on the other side 

 of its center and shows little regularity 

 of sporangial contents. The dark bodies 

 shown are more or less distorted mega- 

 spores lacking their usual regularity of 

 position. If eight megaspores are pres- 

 ent it seems that some of them were 

 abortive. Although this sporangium (h) 

 has not attained normal development, 

 the sporangium below it (c) apparently 

 has grown larger to compensate for this, 

 becoming almost spherical. The six 

 spores shown in sporangium c are also 

 displaced from their usual arrangement, 

 but the increase in the size of the spor- 

 angium is accompanied by an increase 

 in the amount of intra-sporangial tis- 

 sue rather than by the development of 

 more spores. The maximum number of 

 megaspores was probably eight and 

 these probably developed ordinarily 

 from only two original tetrads. The 

 manner in which the individual spores 

 separated from the tetrad and came to 

 be enclosed in tissue is still an unsolved 

 problem, but may be due to anomalous 

 growth of the subarchesporial pad. Hir- 

 mer's suggestion (1927, p. 284) that the 

 eight megaspores developed from eight 

 tetrads with three spores of each tetrad 

 totally abortive, is unsupported by any 

 positive evidence and makes the well 

 developed trilete (haptotypic) structure 

 of each mature spore very difficult to 

 explain. 



A normal sporophyll is shown in plate 

 1, figure 2 (N Sp) cut in almost perfect 

 median section. Its sporangium, how- 

 ever, is separated from the pedicel and 

 apparently was held in place only by 

 the short upturned lamina. From this 

 and similar examples, it is evident that 

 as the cone broke up, the sporangia 

 tended to separate from the pedicels. 

 In Mazocarpon shorense, the entire 

 sporophyll was shed as a unit, so that 

 the separation' of individual sporangia 

 in M. oedipternum, rather than com- 

 plete sporophylls, may also be taken as 

 a specific distinguishing character. The 

 dorsal loop of the sporophyll trace with- 

 in the bulbous heel is plainly shown. 

 The trace passes out of the section prox- 

 imally so that it is not shown entering 

 the axis. However, the proximal portion 

 of a trace is shown by the second sporo- 



