74 PEOCEEDINGS OF THE 



ABSTEACTS. 



Abstbact of Prof. Weiss's Paper on the Morphology of Stig- 

 maria and of its Appendages in Comparison with Becent 

 Lycopodiales. 



[Eead 5tb March, 1908.] 



The opposition to the identification of Stirjmaria as the " root- 

 system" of Sigillaria has gradually disappeared owing to the 

 accumulation of evidence supporting Binney's discovery in 1845 

 of an organic connection between Stigmaria and Sigillaria. 

 But the recognition of this fact and its subsequent extension 

 to the case of Lejndodendron did not settle definitely the morpho- 

 logical value of the Stigmarian axis. It might still be regarded 

 either as a large bifurcating root bearing lateral roots or as 

 an underground stem (rhizome), in which case its appendages 

 might be adventitious roots (Scott) or leaA'es modified to serve 

 absorptive purposes (Solms-Laubach), or possibly both kinds of 

 lateral organs might be present (Renault). Some recent obser- 

 vations have tended to reopen the discussion of the morphology 

 of the appendages, particularly the recognition of peripheral 

 " transfusion " tracheids in the Stigmarian appendages and the 

 presence of a parichnos-strand in these organs. But though both 

 have their counterpart in the leaves of the Lepidodendracese, T can 

 only see analogy and not homology in these structures, and 

 believe their presence is due to the physiological requirements of 

 the organs in question. 



The older objection to the identification of the appendages as 

 rootlets, namely their exogenous origin, is sufficiently answered 

 by the fact that several recent Lycopodiales, such as Phylloglossum 

 and the young sporophyte of Isoetes, have exogenous roots. The 

 regular quincuncial arrangement of the rootlets similar to that of 

 the leaves of the Lepidodendracese might be explained by the fact 

 that we know of rootlets placed close to the base of the leaves of 

 certain Sigillarige (Sigillaria sjnnulosa). 



A suppression of the leaves on the underground axis might 

 leave the rootlets with the same arrangement as the leaves in the 

 aerial portion of the stem. These considerations and the very 

 close agreement in structure of these problematical appendages 

 with the monarcli roots of Isoetes, seem to me strong reasons for 

 regarding the Stigmarian appendages as true roots. 



As regards the axes on which they were borne, their structure, 

 so different from that of the rootlets and so singularly unlike the 

 roots of any living plant, seems to prevent our regarding them as 

 main roots. Their cauline nature has been questioned on account 

 of the difference in their structure from that of the aerial stems of 

 the Lepidodendracese. But recent evidence in confirmation of 

 Renault's observations of the existence of Stigmarice with centri- 

 petal wood partially removes this objection. Still, in the case of 



