FILICALES 





Seed-Plants. The tissues of all their parts originate from segmentation 

 of superficial cells. This is a general character of the Pteridophyta, though 



Fig. 383. 

 Apex of stem of Osmunda regalis, seen from above, 

 showing the three-sided apical cells of stem, and of leaf ; 

 and the bases of the older leaves shaded. The succes- 

 sive segments of the apical cell form the whole of the 

 apical cone. ( x 83). 



Fig. 384. 



Young leaf of Ceratopteris, in surface view, after 

 Kny ; showing two-sided apical cell ; and the 

 marginal series, continuous round the young 

 pinnae. The latter do not correspond in number 

 to the segments from the apical cell. 



the details of their segmentation and the number of the initial cells are open 

 to variation. 



Fig. 385. 



( x 250.) A = longitudinal section through apex of th-> n rans- 



verse section through the apical cell of the root and neighbouring segments of 

 Athyrium. (After Naegeli and Leitgeb.) r = apical cell, k, I. m, n =-successivt- laj 

 of root-cap. o = dermatogen. c = limit of stele. (From Sachs.) 



Thus constituted the Fern-Plant carries out its Life on Land in 

 essentially the same way as Seed-Plants. The structural differences 

 are those of detail, the most important being the absence of secondary 

 thickening in the stem. These plants have no automatic provision for 

 increasing mechanical strength with size. In Tree-Ferns this deficiency 

 is made up for partly by masses of hard brown sclerenchyma. which 



