XXI] ANATOMY 133 



in the Marattiaceae (Fig. 423, A, B). Lastly, the sporangium is very 

 A B 



Fig. 424. Young sporangia of Todea bar- 

 bara in longitudinal section, showing 

 difileren t mod es of segmentation . ( x 363 . ) 



Fig. 423. A, median longitudinal section through the root-tip of Osmunda regalis showing 

 two truncated initials ( x ), segments being cut off from both ends as well as from the sides. 

 ( X 200.) B, transverse section through the root-tip of Todea barbara, showing four initials 

 ( X ), and the principal walls /./. ( x 200.) Both were taken from large roots of adult 

 plants. 



inconstant in its cleavages, and is not always referable to the segmentation 

 of a single cell. Moreover, the sporogenous 

 cell may sometimes be cubical, as in the 

 Eusporangiatae, but more frequently it is 

 tetrahedral, as in the Leptosporangiatae 

 (Fig. 424). All these facts show that the 

 Osmundaceae are unstable in their seg- 

 mentation : that they conform decisively 

 neither to the Eusporangiate nor to the 

 Leptosporangiate types, but hover between 

 the two. This conclusion acquires special significance when the very early 

 fossil history of the Family is remembered. 



Anatomy 

 The massive upright stock of the Osmundaceae, so closely invested by leaf- 

 bases each with its sclerotic sheath and containing a densely sclerosed 

 cortex, is very difficult to cut, and its appearance in section as a whole is 

 better known from sections of the related fossils than from published figures 

 of living stems. A large stock of Todea (^Leptopteris) Fraseri from the Blue 

 Mountains, Australia, was cut transversely, and its surface polished as an 

 opaque object. Its appearance is seen in Fig. 425. At the periphery are the 

 brown remains of the outer leaf-bases together with matted roots. Next 

 follows a broad band made up of leaf-bases each with its C-shaped meristele 

 embedded in soft parenchyma, which is delimited by a dark sclerotic sheath. 



