The Affinity of Tmcsipteris with the Sphenophyllalcs. 343 



" The Affinity of Tmesipteris with the Sphenophyllales." By 

 A. P. W. THOMAS, M.A., F.L.S., University College, Auckland, 

 New Zealand. Communicated by Professor G. B. HOWES, 

 F.R.S. Received January 6, Read January 23, 1902. 



The peculiar fertile structures of Tmesipteris and Psilotum have given 

 rise to much discussion as to their morphological nature. The foliage 

 leaves in Tmesipteris, as is well known, are simple, whereas the fertile 

 structures are forked, that is, each has a stalk bearing leaf-like lobes, 

 a bilocular sporangium or synangium being attached to the stalk just 

 below the lobes. 



Three views have been taken as to the nature of these fertile 

 structures 



1. The whole structure has been interpreted as a branch of the 



stem, being equivalent to a reduced Lycopodium spike. The 

 lobes, according to this view, will be leaves. (Juraniyi, Stras- 

 burger, Sachs, Goebel.) 



2. It has been considered as equivalent to a single leaf. Brongniart 



and Luerssen compared it with a Lycopodium sporophyll. 

 Professor Bower, as the result of his investigation of the 

 development of the organs of Tmesipteris, regarded it as a 

 " single leaf with two lobes, bearing the synangium on its 

 adaxial face."* He considered the synangium to be a septate 

 sporangium. 



3. Dr. Scott considers that an at least equally probable explana- 



tion is, that the synangium with its axis may correspond to 

 the ventral sporangiophore of the Sphenophyllales. t 



I propose to adduce evidence to show that whilst Professor Bower's 

 view that the whole fertile structure of Tmesipteris is equivalent to a 

 single leaf is correct, Dr. Scott's suggestion that the synangium, with 

 its axis, corresponds to a ventral sporangiophore, is also correct. 



Professor Bower speaks of the whole fertile structure as a sporan- 

 giophore, whereas Dr. Scott would restrict the term sporangiophore 

 to the synangium and its axis, referring to the Sphenophyllales, in 

 which sporangiophores spring from the iipper surface of bracts as long 

 pedicels, bearing one or more sporangia at their ends. To avoid con- 

 fusion, 1 propose to speak of the whole fertile structure as a fertile 

 leaf or sporophyll, and will use the term sporangiophore in the sense 

 of Dr. Scott and Mr. Seward. 



The evidence I have to offer is derived from the study of the varia- 

 tions which occur in the sporophylls. These variations are of striking 



* 'Phil. Trans.,' B, 1894. 



t ' Studies in Fossil Botany,' p. 499. 



