36 



CONCLUSION 



tween the two groups, and until we 

 have real evidence that Spencerites is 

 either heterosporous or homosporous, 

 surmises are not warranted. Scott, at 

 one time at least, entertained the pos- 

 sibility that Spencerites insignis might 

 have some sigillarian connection, al- 

 though no proof of this or any other 

 alliance has been forthcoming. ^^ 



The notable features of Spencerites 

 which may be compared with Mazocar- 

 pon are : ( 1 ) The cones in both genera 

 are pedunculate with the peduncle of 

 Spencerites bearing ''irregular bracts" 

 somewhat as in M. oedipternum; (2) the 

 cone axis sometimes has a ''pith" and 

 sometimes is solid in individual species 

 of both genera; (3) sporophylls of 

 Spencerites have not yet shown any 



trace of a ligule; in M. oedipternum 

 the presence of a ligule is hard to dem- 

 onstrate although it has been found in 

 a few instances. Although theoretical 

 interpretation would hold that the ligule 

 of M. oedipternum is probably always 

 present this is not proved, and the re- 

 ported absence of a ligule in Spencerites 

 may also be because it is ephemeral and 

 hard to find;^^ (4) the sporophylls of 

 Spencerites may vary in arrangement 

 from spiral to verticillate in the same 

 manner as has been described for M. 

 oedipternum (cf. Berridge, 1905, p. 

 275). Such phyllotactic variability is 

 often present among modern lycopods, 

 consequently neither this similarity nor, 

 in fact, any of the others just men- 

 tioned, can be taken as necessarily sug- 

 gestive of phyletic alliance. 



CONCLUSION 



Mazocarpon oedipternum clearly indi- 

 cates from its geological position that 

 the Mazocarpon type of sigillarian fruc- 

 tification existed at least throughout 

 most of Pennsylvanian time. During 

 this period it seems unlikely that any 

 sigillarian fructifications deviated very 

 much from the Mazocarpon type, but 

 specimens preserved as compressions 

 (Sigillariostrohus) probably are not en- 

 tirely corgeneric although they may co- 

 incide for a considerable part of their 

 respective geologic time ranges. Evi- 

 dence from several sources shows the 

 overlapping relationship of these gen- 

 eric groups, and similar types of evi- 

 dence link them definitely with Sigil- 

 laria. However, as frequently is the 

 case for fossil plant material, conclusive 

 evidence is lacking for species. Thus, al- 

 though the assignment of these genera 



"The discussion of the relationship of Spencer- 

 ites and other forms given by Watson in 1909 

 does not accord with historical facts as known 

 at present. For example, Lepidostrohus kentucky- 

 ensis Scott and Jeffrey is from the uppermost 

 Devonian, according to recent studies by C. B. 

 Read (Read and Campbell, 1939). Evidently 

 therefore, Lepidostrohus cannot be regarded as a 

 derivative of the much younger forms of Spen- 

 cerites and Mesostrohus from beds equivalent to 

 the lower Pennsylvanian in age. If there is any 

 direct phyletic connection the sequence must be 

 reversed from that which Watson suggested, Lepi- 

 dostrohus shows no characters indicative of a 

 highly advanced type but represents chiefly en- 

 largement of a primitive heterosporous type of 

 cone. The writer considers it less advanced than 

 the relatively primitive but modern genus Selag- 

 inella. 



to a "sigillarian alliance" may hardly 

 be questioned in its broader aspects, the 

 species nomenclature should remain es- 

 sentially the same; if anything the 

 species should be more strictly defined. 

 The sigillarian alliance thus outlined 

 probably has little relationship in com- 

 mon with the lepidodendrids of the 

 period despite similarities in many an- 

 atomical details. Lepidocarpon shows 

 no close phyletic relationship to Mazo- 

 carpon but instead represents a parallel 

 line of specialization tracing back his- 

 torically as far as Mazocarpon itself. 

 Lepidostrohus is a plant group, of lepi- 

 dodendrid alliance, which lacks the 

 sporangial elaboration shown in differ- 

 ent ways by Lepidocarpon and Mazo- 

 carpon. Lepidostrohus is present in the 

 American uppermost Devonian, accord- 

 ing to Read and Campbell (1939), and 

 thus is the most ancient representative 

 of the groups mentioned. Probably the 

 two specialized lines originated from 

 this unspecialized (but geologically per- 

 sistent) lepidostrobid stock early in 

 Mississippian time, although it may 

 have been still earlier. Considerable 

 interest attaches to definition of the 

 specialized groups in the Mississippian 

 in view of their probable phyletic deri- 



^Actually very few specimens of Spencerites 

 cones have been studied. 



