568 CYCADOPHYTAN FRONDS [CH. 



of the veins are characters in which Nilssonia differs from Taenio- 

 pteris. The veins are given off at right-angles or obliquely from 

 a very narrow groove occupying the median line of the rachis; 

 they are nearly always simple and in some of the more fleshy 

 leaves, e.g. N. brevis, they are seldom visible. The surface of the 

 lamina may be smooth or transversely corrugated. The rachis 

 forms a prominent rib on the under surface of the frond (fig. 620, A) 

 and may be continued beyond the lamina as a short petiole. 

 Epidermal cells polygonal or rectangular, with straight walls in 

 contrast to the sinuous walls of Taeniopteris ; some of the cells 

 bear strongly cuticularised papillae, possibly the bases of hairs 

 (compare the hairs on the fronds of Acrostichum crinitum, a Fern 

 with leaves similar in shape to some of the large entire fronds of 

 N. orientalis though relatively broader and with anastomosing 

 veins). Stomata usually confined to the lower epidermis and 

 not very numerous ; guard-cells of rounded contour and without 

 any special thickening surrounded by 6 8 accessory cells with 

 thickened walls (fig. 611, B) forming a chimney slightly raised over 

 the stomatal pore 1 . In Nilssonia the guard-cells do not exhibit 

 that regularity of orientation which characterises the stomata 

 of Ptilophyllum, Otozamites, and other Bennettitalean fronds. 

 Little is known of the anatomy of the leaves : in a petrified leaf 

 of N. orientalis 2 from Upper Cretaceous rocks in Japan there is 

 no palisade-tissue and small groups of sclerenchyma occur above 

 and below the veins. The xylem appears to be centripetal, but 

 the preservation is far from satisfactory. A few secretory canals 

 were found near the edge of the leaf. We have no certain know- 

 ledge of the reproductive organs. The small circular projections 

 figured by Schenk 3 on some leaves of Nilssonia polymorpha as 

 sporangia have no claim to be so regarded. In the description 

 of N. brevis reference is made to some seeds discovered by Nathorst 

 which may belong to that species. Nathorst suggests the possi- 

 bility that the Khaetic fossil Stenorrachis scanicus Nath. may be 

 the seed-bearing shoot of a Nilssonia, either N. brevis or TV. poly- 

 morpha, and if this surmise is correct it almost necessarily involves 

 the genus Beania* which has been tentatively referred to the 



1 Nathorst (09 2 ); Thomas and Bancroft (13). 2 Stopes (10 2 ). 



3 Schenk (67) A. PI. xxix. figs. 1, 2. 4 See vol. iv. 



