The Present Position of Palaeozoic Botany. 



185 



It is obviously diflicult to obtain conclusive proof that a given 

 fructification represents the sporangia of a Fern, and not the micro- 

 sporangia of a Pteridosperm. Our information as to the latter class 

 of organs is still so imperfect that we cannot tell how Fern-like they 

 may sometimes have been. In the Botryopterideae and in such fructi- 

 fications as Pteridotheca WiUianisoni, the presumption, however, is all 

 on the Fern-side, 



In two cases a remarkably fortunate accident of preservation has 

 provided us with more decisive evidence. In 190-1: I described an 

 instance of ''Germinating Spores in a fossil Fern-sporangium" (Scott, 

 1904). The sporangium is a detached one and there was at the time 

 nothing to indicate the plant to which it belonged. The sporangial 

 wall is several cells thick; there is no definite annulus, though the 

 cells of the external layer are larger on one side of the sporangium 

 than elsewhere. The spores were evidently germinating actively 

 when fossilization took place, germination going on within the 

 sporangium, as not infreciuently happens, under exceptional conditions, 

 in recent Ferns. Various stages are shown; in some a long rhizoid 

 has been protruded, in others the first cells of the prothallus are 

 formed, in others, again, both prothallus and rhizoid are present. 

 The stages are exactly similar to those seen in the germination of 

 the spores of recent homosporous Ferns. 



Fig. 15. Stauro'pteris oldhamia. Three sporangia, attached to ultimate branches of 



the rachis. In A, the stomium, st is shown. B is cut tangentially. In C, j; is 



palisade-tissue of the rachis. X about 35. 



A year later I was able to describe the sporangia of Stauropteris 

 oldhamia (Scott, 1905) which are found attached terminally on the 

 fine branches of the rachis (Fig. 15). This fossil is w^ell known from 

 Williamson's description (Williamson, 1874); it consists of a 



