628 STUDIES IN FOSSIL BOTANY 



The comparison with Ophioglossum was also empha- 

 sized by Mettenius and Solms-Laubach, and from a 

 purely morphological point of view appears to be well 

 justified. The groups Psilotaceae and Ophioglossaceae 

 are, however, so widely divergent in their other 

 characters, that any affinity between them must be 

 remote in the extreme. In the Sphenophyllales, on 

 the other hand, we have a group, with which, as we 

 have seen, the Psilotaceae have other characters in 

 common. In the Sphenophylls the sporangia are borne 

 on a ventral outgrowth of the bract or sporophyll, each 

 fertile outgrowth having its own vascular supply, arising 

 as a branch-strand from the bundle of the dorsal bract. 

 In Tmesipteris (the less reduced of the two genera 

 of Psilotaceae) the agreement with Sphenophyllum 

 is clear. A leaf- trace passes out from the stele 

 and enters the base of the sporophyll, where it 

 divides into three (Fig. 213, B). Two of the branch- 

 strands enter the two forks of the sporophyll, while 

 the third turns upwards, passes through the pedicel of 

 the synangium, and extends into the septum between 

 its two constituent sporangia 1 (Fig. 213, A). Thus 

 the position of the pedicellate synangium and its 

 anatomical relation to the subtending sporophyll 

 correspond exactly to the conditions in the Spheno- 

 phyllales. The comparison, originally pointed out in 

 my paper on Cheirostrobus in 1897, and further em- 

 phasised in the first edition of these " Studies " (p. 490) 

 has received valuable support from the observations of 

 Professor Thomas, 2 of Auckland, New Zealand, who has 



1 For some more detailed observations see below, p. 631. 

 " A. P. W. Thomas, "The Affinity of Tmesipteris with the Spheno- 

 phyllales," Proc. Royal Society, vol. lxix. 1902, p. 343. 



