

The Affinity of Tnii>xif>tn-ix with tlie, SphtnophyllaleS. 347 



Leaving on one side obvious comparisons as regards some of these 

 characters with certain ferns, I would venture to suggest that it is in 

 the extinct Sphenophy Hales that we find the closest morphological 

 parallel with the sum total of the characters now shown for 

 Tmesipteris. The leaves in Sphenophyllum were frequently hetero- 

 morphic. A common type of leaf was a wedge-shaped one, but it is 

 important to notice that the veins were dichotomously divided, and 

 the margin of the leaf frequently more or less notched or lobed in 

 accordance with the venation. But the leaves varied much in form, 

 from such as have been described to leaves with a lamina dissected 

 into dichotomously branched linear segments, or to simple narrow 

 uninerved leaves.* In 8. cuneifolium the upper cone-bearing branches 

 show the finely cut foliage, whilst in some specimens entire and much 

 divided leaves occur mixed together in the same specimen. 



But it may be objected that such leaves are foliage leaves, whereas 

 it is the sporophylls which alone are forked in Tmesipteris. The 

 sporophylls of Sphenophyllum formed strobili, as a rule sharply 

 marked off from the foliage-bearing regions, but in *S'. trichomatosum 

 the cones were very lax, and not sharply marked off.f In the well- 

 known form S. Duwsoni, the bracts were simple, but in others they 

 were forked. In S. tenerriminn the cones were small, but the bracts 

 narrow and dissected. 



The force of the comparison with the Spenophyllales is of course 

 intensified if it be admitted that the variations recorded above for 

 Tmesipteris prove that the synangium is equivalent to a sporangio- 

 phore with its sporangia. 



In Sphenophyllum Dawsoni each bract carried two sporangiophores on 

 its upper surface, each sporangiophore bearing a single pendulous 

 sporangium. But in the Bownmnites lioi'uit'ri each sporangiophore 

 bears two sporangia. If we may trust the variations recorded under 

 Group 2 above, we have here a surprisingly close correspondence 

 between Bowmanites and Tmesipteris. But some species of Spheno- 

 phyllum present evidence of as many as four sporangia to a single 

 sporangiophore. I have occasionally found trilocular synangia in 

 Tmesipteris, as, indeed, others have done ; whilst in Psilotum the 

 number of loculi, though normally three, may vary from two to five. 



Perhaps one of the most interesting forms for comparison with 

 Tmesipteris is the cone described by Scott under the name of Cheiro- 

 strobus, and shown by him to belong to the Sphenophy Hales, f In 

 Cheirostrobus the sporophylls are very elaborate; each is divided 

 nearly to its base into three lower sterile segments and three upper 

 fertile segments or sporangiophores. May we compare a sporophyll of 



Seward, ' Fossil Plants,' vol. 1, p. 391. 

 t Scott, ' Studies in Fossil Botany,' p. 105 ; 

 I Scott, ' Phil. Trans.,' B, 1897. 



2 B 2 



