VI] 



SEGMENTATION IN EUSPORANGIATE FERNS 



113 



system of construction, which the single apical cell itself represents according 

 to Sachs, is here less complete. The principal and sextant walls do not stop 

 short in the segments already cut off from the initial, but are actually con- 

 tinued upwards so as to take part in defining the three initial cells themselves 

 and their segments. The system of construction of the Osmundaceous root 

 is seen to be more complete than in any of the ordinary Leptosporangiate 

 Ferns. Thus the Osmundaceae, while conforming in some degree to the 

 Leptosporangiate segmentation, show in several details a more complex 

 condition than they. 



B 



Fig. III. A, i) = transverse sections of the root-tip of Osimmda regalis, 

 showing anomalous structure with three initials {x). Compare the 

 position of these, the principal walls (/,/), and the sextant walls {s,s), 

 with those seen in Fig. 102 of D. pjDutilobiila. 



Still more is this to be observed in the Marattiaceae. In well-grown 

 stems of Angiopteris and Marattia a single initial cell has not been found. 

 In its place there are arrangements which 

 indicate three or four initials (Fig. 112). 

 But stems of young seedlings oi Marattia 

 alata have been found to have a single 

 irregular initial with early transition to 

 more complex structure (Charles (105), 

 PI. Xl). Longitudinal sections show the 

 conical or prismatic initials to be very 

 narrow and deep, suggesting a deeply 

 sunk centre of construction of the system 

 of curves. Similarly in their leaves, 

 though a single initial may appear in 

 those of the sporeling, in older leaves, 

 as in the stem, a plurality of initials is 

 found. In the development of the mas- 

 sive wings of these leathery leaves there is no definite marginal series, but 

 as in the Osmundaceae a small-celled meristem (Fig. 109, A). The apices of 



Fig. 112. ^=apex of stem o[ Angiopteris 

 evecta, seen from above. Apparently there 

 are four initials {X, X). { x 83.) 



