528 FILICALES 



The late definition of the parts of the embryo is in accord with the 

 indefiniteness of the apical segmentation of these Ferns. There are some 

 though inconstant signs of a single initial cell in the apex of root and stem of 

 the embryo ; but the apices of the mature parts of the Marattiaceae, whether 

 axis, leaf, or root, show as a rule a more complex structure, three or 

 more commonly four initial cells being recognised. This arrangement of 

 the meristems is in accord also with the Eusporangiate character of these 

 Ferns. Many years ago 1 I showed that a parallelism exists in the Filicales 

 between their sporangial origin and the meristems of all the vegetative parts; 

 that in the Leptosporangiate Ferns, where the whole sporangium originates 

 from a single parent cell, the apical meristems of stem, leaf, and root are 

 referable also to the segmentation of a single initial cell ; but that in the 

 Eusporangiate Marattiaceae the apical meristems are more complex, with 

 no single initial. With this goes also the deeply sunk character of the 

 sexual organs on the prothallus. Thus the general conclusion must be 

 that in all its parts the Marattiaceous type differs from the Leptosporangiate 

 type in its greater robustness of construction. 



The account given in the preceding pages includes facts which show 

 good reason for holding to the early existence of plants of a Maratti- 

 aceous type. Not only does this follow from the detailed comparison of 

 Pecopterid-sori with those of the living Marattiaceae, but also from the 

 structure of the Psaronius-stems. From evidence of comparative structure 

 and association it appears certain that the Psaromus-stems bore the foliage 

 of Pecopteris of the same nature as the leaves on which various synangic 

 fructifications have been found. Thus we have to do with a group of 

 Palaeozoic fossil-plants showing affinity with the Marattiaceae alike in their 

 anatomical structure and in their reproductive organs. But certain fructi- 

 fications previously classed as Marattiaceous have lately been shown to be 

 the pollen-apparatus of Spermophytes, e.g. Crossotheca and Pecopteris (Dick- 

 sonites) Pluckeneti. Considering the anatomical evidence, however, it seems 

 impossible to doubt that Palaeozoic Marattiaceae actually existed, for the 

 Psarom'us-type of stem is altogether Fern-like in structure, and presents 

 none of those anatomical features by which the Cycadofilices were recog- 

 nised long before the evidence of fructification led to the foundation of 

 the class Pteridospermeae. For the present, therefore, we must continue 

 to accept the existence of a certain number of Marattiaceous Ferns, 

 especially in the later Carboniferous and Permian periods, though we may 

 not always be able to distinguish their fructifications from the pollen- 

 bearing organs of Fern-like Seed-Plants. It seems not improbable that 

 Marattiaceae and Pteridospermeae may .have owed their synangic fructi- 

 fications to some common descent from a primitive group of Filicales in 

 which that character had already appeared.' 2 



1 Ann. of Bot., 1889, vol. iii., p. 305. 



2 This paragraph is taken almost verbally from Scott, "Present position of Palaeozoic 

 Botany," Progressus Rei Botanicae, 1907, pp. 187-189. 



