NILSSOXIA. 51 



two different kinds of veins in the leaf divisions. Schenk, in 

 his Flora der Grenzschichten 1 includes Nilssonia among the ferns, 

 and refers to certain specimens in which the leaves show 

 numerous round projecting structures between the veins, and 

 which he regards as sporangia or sori ; and it is on the strength 

 of these appearances, suggestive of fern fructification, that the 

 genus is excluded from the Cycadacece. Schenk speaks of the 

 veins as equal and simple, and refers to the epidermal cells as 

 having the straight walls characteristic of cycads. No great 

 importance should be attached to any argument based on the 

 form of the cell walls, as Schenk himself has admitted ; but 

 the fructification is a much more important feature. Saporta 2 

 places Nilssonia in the Cycadacece, and considers that Schenk 

 was probably deceived by certain leaf parasites, which might 

 well present an appearance closely simulating fern sori. Nathorst 3 

 follows a similar course, and speaks of our ignorance as to 

 the actual nature of Schenk's sori, seeing that no traces of 

 structure have been preserved ; he suggests stomata and parasitic 

 fungi as two possible explanations of these sorus-like appearances. 

 Solms-Laubach 4 does not accept the proposed explanation as 

 satisfactory, and inclines to follow Schenk in classing Nihsonia 

 among the ferns, on the strength of the sorus-like bodies on the 

 leaf lamina. JSTathorst draws special attention to the insertion 

 of the leaf segments on the upper surface of the rachis as an 

 essential character of the genus; he speaks of the veins as equal 

 and simple. Various authors have spoken of two kinds of veins 

 in the leaves of Nilssonia, stoiiter and finer veins, but Nathorst 

 remarks that Schenk has recognized his mistake with regard to 

 the supposed two sets of veins ; he mistook folds in the leaf 

 lamina for well-marked simple veins. 5 Schimper, 6 in the first 

 volume of the Trait, pal. veff., classes Nilssonia with the 

 Filicince, and accepts Schenk's interpretation of the apparently 



1 (A. 1), p. 124. 



* (A. 2), Pal. Fran^. vol. ii. p. 41. 



3 (A. 2), Foss. Fl. Schwedens, p. 20. 



4 Fossil Botany, p. 139. 



5 Nathorst (A. 2), p. 18. 



6 p. 488. 



