VIII 



MARATTIALES 



2&7 



'I 



..--2^ 



older parts of the root to the segments of the apical cell is 



impossible to determine, and evidently is not always exactly 



the same. The root-cap is derived mainly from the outer 



segments of the apical cell, but also to some extent from the 



outer cells of the lateral segments; and the central cylinder, 



where the base of the 



apical cell is truncate, is ^^\ St A. 



formed mainly from the 



basal segments, but in 



part as well from the 



inner cells of the lateral 



segments. 



The vascular cylin- 

 der of the root is usually 

 tetrarch. At four points 

 near the periphery small 

 spiral or annular 

 tracheids appear, and 

 from them the formation 

 of the larger secondary 

 tracheids proceeds 

 toward the centre. The 

 phloem is made up of 

 nearly uniform cells with 

 moderately thick colour- 

 less walls. A bundle- 

 sheath is not clearly to be 

 made out (Fig. 156). 



The cotyledon is des- 

 titute of the stipules 

 found in the perfect 

 leaves of the Marat- 

 tiaceae, but they are well 

 developed in the third 

 leaf, where they form 

 two conspicuous append- 

 ages clasping the base 



of the next youngest leaf. The edges of these stipules are 

 somewhat serrate, and the edges of the two meet, much like two 

 bivalve shells. The strictlv dichotomous character of the 

 cotyledon is gradually replaced in the later leaves by the pinnate 



Fig. 159. — Marattia Doiiglasii. A, Longitudinal 

 section of the young sporophyte, showing the 

 distribution of the vascular bundles, X6; /, 

 leaves; sf, stem apex; r, a root; f, the foot; 

 B, young sporophyte with the prothallium 

 (pr), still persisting. 



