The Present Position of Palaeozoic Botany. 163 



III. Psilotales. 



It is not my purpose, under the above heading, to discuss the 

 highly doubtful fossils, such as Fsiloplujton and Gomphosfrohus, which 

 have sometimes been referred to the Psilotaceae, but rather to con- 

 sider the affinities of the recent group in the light of our knowledge 

 of the Palaeozoic Sphenophyllales. The two points on which the 

 question turns are the anatomy of the stem and the morphology of 

 the sporophyll. As regards the anatomy, it has already been pointed 

 out that Psilotum presents a nearer analogy with the Sphenophyllales 

 than any other recent plant, the resemblance being most marked in 

 those branches where the stele is triarch and the xylem extends to the 

 centre. The discovery by Boodle that, at the base of the aerial stem 

 and in adjoining parts of the rhizome of Psilotum, a well-marked for- 

 mation of secondary wood may take place in old plants, strengthens 

 the anatomical analogy in a striking manner. The anatomy by it- 

 self, howevei', would go for comparatively little, considering that ana- 

 tomical resemblances between the Psilotaceae and certain recent and 

 fossil Lycopods are also evident. We must now examine the evidence 

 aiforded by the reproductive organs. 



The nature of the synangium of the Psilotaceae has long been 

 in dispute. While the earlier botanists, influenced no doubt by the 

 prevailing tendency to compare reproductive organs with buds, regarded 

 the synangium as an axillary structure, Brongniart, in 1836, first 

 pointed out its epiphyllous position. Since then there have been two 

 principal views of the nature of the Psilotaceous sporangium, that of 

 Mettenius, Luerssen, Celakovsky, Solms-Laubach and 

 Bower, who regarded it as the direct product of the subtending 

 leaf, and that ofJuranyi, Sachs, Strasburger, Goebel and 

 Bertrand, who held that the synangium represents a fertile branch, 

 of which the two first leaves are fused to form the forked bract. The 

 latter view demands the assumption that the sporophylls are entirely 

 suppressed, a condition for which it would be difficult to find an 

 appropriate analogy. 



On the foliar view the forked bract is itself the sporophyll. While 

 some authors, and notably Bower, have interpreted the sjmangium 

 simply as a sporangium which has become septate, Celakovsky has 

 regarded it as representing a fertile, ventral lobe of the sporophyll, 

 comparable to the spike of Ophioglossum, a view which is more in 

 harmony both with the structure and the development. The comparison 

 with Ophioglosseae was also emphasized by Mettenius and Solms- 

 Laubach, and from a purely morphological point of view is an 

 eminently fertile one. There can scarcely, however, be any question 



11* 



