A FEKN FORMING A NEW GENTJS — ETHEHIDGE. 143 



SO that here alone among Ferns the bundles are capable of second- 

 ary thickening. The whole cylinder is enclosed by a bundle-sheath 

 (endodermis) consisting of a single layer of cells. The cortical 

 part of the stem is mainly composed of starch-bearing parenchyma, 

 but the outermost layers show a formation of cork." An excellent 

 diagramatic sketch of the several parts accompanies these remarks. 



I believe PI. xxvi., tig. 10, to practically represent the greater 

 portion, if not all, of the stem or caudex, viewed transversely. It 

 will be noticed that the central portions retain a fairly continuous 

 oval contour, but the outer portions, possibly from extraneous 

 causes, have been crushed together, and the contour broken or 

 distorted. The dark centre in our figure, and from which the 

 whole structure in the specimen has been obliterated, represents 

 without doubt the pith (there is no evidence of primary wood), 

 whilst the zone surrounding this is the secondary wood or xylem. 

 The two outer rings in PI. xxvi., tig. 10, judging by Dr. Campbell's, 

 may possibly represent — the inner one the endodermis, and the 

 outer the cork formation of the parenchyma. These rings in the 

 fossil are of a dark orange-brown colour. In the enlarged figure, 

 (PI. xxvi., fig. 11) the dark radiating lines perhaps represent the 

 medullary rays. 



The following measurements were kindly made by Mr. T. 

 AVhitelegge : — 



Longer diameter of caudex I'S mm. 



Shorter ,, ,, 1'2 ,, 



Diameter of pith .• 0-35,, 



Width of ring of secondary wood 0-25 ,, 



Space between exo- and endoderm O'l to 0"2 mm. 



Space between endoderm and secondary 



wood 0-0 to 0-1 „ 



Width of exoderm 04 mm. 



Width of endoderm 003 ,, 



In a longitudinal section of the caudex (PI. xxvii., fig. 12) the 

 same number of zones can be distinguished as in a transverse 

 section (PL xxvi., fig. 10). Thus, the central cylinder, without 

 structure, is followed by the zone of secondary wood, in which 

 faint longitudinal parallel lines can be discerned, answering to the 

 radial lines in Plate xxvi., figs. 10 and 11, but no minute details 

 can be made out. The edge of the secondary wood is of the same 

 deep amber-brown colour already referred to in other parts of the 

 organism, and between this and the layer corresponding to the 

 endoderm in Dr. Campbell's diagram of the stem in Botrychiuni, 

 is a further narrow structureless zone (the inner of the two in 

 PI. xxvi., fig. 10), that varies so much in radial diameter. The 

 endoderm and the exoderm are again of a deep amber-brown tint, 

 and form strongly marked features of the section, the intermediate 



