MARATTIACEAE 



527 



The cortex which surrounds the central region in the fossil stems was 

 traversed by large numbers of downward-growing roots, having characteristic 

 Marattiaceous structure : the cortex with its contained roots was often 

 distended to great bulk, while outside it a mass of densely woven roots 

 is sometimes seen. It seems probable that these specimens represent 

 the basal region of arborescent stems, which, though greater in stature 

 than the living forms, were Marattiaceous in their characters. Not only 

 is this so as regards general structure, but also in the details of the tissues, 

 into which, however, it is impossible to enter fully here ; l the recognition 

 of their affinity with the modern Marattiaceae is thus further confirmed. 



A hi 



EMBRYOLOGY. 



The embryology of the Marattiaceae shows features distinct from that 

 of other Ferns. The prothallus is of the normal flattened Fern-type. 

 though of larger size and more massive 

 construction. The sexual organs are 

 borne on its under side, and are deeply 

 sunk in its tissue, not projecting from its 

 surface, as in the Leptosporangiates. 

 The first segmentation of the zygote is 

 by a basal wall transverse to the axis 

 of the archegonium, whereas in most 

 Ferns it is nearly coincident with it 

 (b, b, Fig. 292 A). The basal wall is 

 followed by segmentation into octants, B 

 and the relation of the parts of the 

 embryo to these is essentially similar to 

 what is seen in other Ferns : the epibasal 

 hemisphere, here turned away from the 

 archegonial neck, forms the cotyledon 

 and the apex of the stem : the hypobasal 

 hemisphere contributes the root and 



foot (Fig. 202 A). But here the Segmeil- Marattia Douglasii. A= longitudinal 



. section of a youn.u embryo. X22$. 6. = the 



tatlOll proceeds further before the Several basal wall; the arrow points to the neck of the 



archegonium. /> = a similar section of an older 



parts are defined than IS the case m the embryo, showing its position in the prothallus. 



- of arche- 



FIG. 292. 



._. , j 



Leptosporangiate Ferns (rigs. 292 B), and g0 nium. x ?2 . (After Campbell.) 

 especially the foot is not clearly limited 



at first, nor does it develop later to any considerable size. The 

 cotyledon and the axis grow directly upwards, surrounded by prothallial 

 tissue forming a calyptra, which projects upon the upper surface of the 

 prothallus : this is finally ruptured, and the cotyledon emerges upwards. 

 Meanwhile the root developing from the hypobasal half emerges downwards, 

 and the prothallus is thus transfixed by the young sporophyte (Fig. 277). 



1 Rudolph, Psar<ii<i und Marattiaceen, \Yk-n, 



