26 



GROUP RELATIONSHIPS 



characteristic of Sigillariostrohus, dis- 

 tinguishing it from Lepidostrohus, is 

 that cones in the latter genus are term- 

 inally attached to ordinary leafy twigs, 

 whereas in Sigillariostrohus the cones 

 are borne on the specialized peduncles. 

 The general correlation of such cones 

 with sigillarian stems showing the scars 

 where cone peduncles were formerly at- 

 tached is adequately supported. At a 

 few horizons (cf. Zeiller 1884) even a 

 specific correlation of stems and cones 

 has been attempted. The specific evi- 

 dence is not altogether conclusive, how- 

 ever, and even if it were, the pertinent 

 question as to the duration in coinci- 

 dence of certain specific features of the 

 cones with other specific features of the 

 stems would still be unanswered. The 

 correlation of Mazocarpon with Sigil- 

 laria, is based on evidence comparable 

 to that which applies to Sigillariosfrohus. 



The manner in which cones of Lepi- 

 dostrohus are borne is similar to that 

 found in modern Selaginella and more 

 advanced species of Lycopodium. This 

 mode of fructification nevertheless is 

 far more primitive, so far as relative 

 specialization is concerned, than the 

 pedunculate mailner of fructification 

 noted in the sigillarians. Variations of 

 this sort are recognized as important 

 wherever they are noted in stu.dy of 

 modern plants; they probably are sim- 

 ilarly reliable indicators of specializa- 

 tion in the Paleozoic flora. The special- 

 ized fruiting habit of Pennsylvanian 

 sigillarians seems well established and, 

 in conjunction with other advanced fea- 

 tures, may be taken to indicate that this 

 sigillarian alliance represents an entire- 

 ly distinct group of lycopods during the 

 Pennsylvanian period. 



Whenever evident, peduncle scars 

 generally occur abundantly in short 

 zones upon the stems of Sigillaria. This 

 may be taken to indicate some sort of 

 periodicity in fruiting. Whether it was 

 coordinated with climatic or seasonal 

 periodicity, like the growth ring special- 

 ization of modern plants, is unknown, 

 but it is reasonable to suppose that it 

 was at least connected indirectly, indi- 

 cating specialization which is not as dis- 

 tinctly shown by other groups of Pale- 

 ozoic lycopods. 



Information is scant in regard to the 

 fruiting habit of Lower Carboniferous 

 sigillarians. It would be expected that 

 at some time in the early history of the 

 groups, specialized cone-bearing ped- 

 uncles would be much less in evidence. 

 No knowledge of the cone axis or ped- 

 uncle of Mazocarpon pettycurense 4s 

 available. If it should prove to be non- 

 pedunculate, its generic segregation 

 from Mazocarpon might be advisable. 

 It is evident that the fruiting habit of 

 Pennsylvanian sigillarians is a heritable 

 and consistent characteristic which is 

 at least of generic significance. 



Stems of the sigillarians may not indi- 

 cate conclusively the mode of fructifi- 

 cation, due to the unequal distribution 

 of peduncle scars. Consequently this 

 character is of less practical value in 

 classification of stem specimens, but the 

 peduncle is often shown by good speci- 

 mens of cones and is more useful in 

 their classification. 



Proof of the real overlapping rela- 

 tionship of Sigillariostrohus with Sigil- 

 laria has been most convincingly shown 

 by Zeiller. Cone peduncles bearing aci- 

 cular bracts and bract-scars which re- 

 sembled those on certain associated Sig- 

 illaria stems seem to be fairly conclu- 

 sive. It now appears (relying on de- 

 scriptions extending over about a cen- 

 tury) that more emphasis can be placed 

 on lack of conflicting evidence than on 

 the positive evidence which supports 

 this general conclusion. Existing evi- 

 dence is based on association and on 

 resemblance between peduncle bract- 

 scars and stem leaf -scars — a comparison 

 which probably is not altogether satis- 

 factory because the bracts and leaves 

 were not entirely similar and no doubt 

 produced cicatrices which were some- 

 Avhat different, even on the same plant. 



Proof of a similar relationship be- 

 tween Mazocarpon and Sigillaria is de- 

 rived chiefly from comparison of pe- 

 duncular steles preserved within sigil- 

 larian stems and in Mazocarpon cone 

 axes and peduncles. This relationship 

 in no way conflicts with other informa- 

 tion pertaining to the relationship of 

 Sigillariostrohus. The basis for consid- 

 ering that Mazocarpon possesses the 

 same sort of relation to Sigillaria that 



