XVI FOSSIL ARCHEGONIATES S8S 



studied by Scott (i). These had Fern-Hke foliage, arid the 

 structure of the stem was also like that of the Ferns, but there 

 was a marked secondary thickening of the stem, such as is rare 

 in Hving Ferns, but is known in the larger species of Botrychi- 

 um. The structure of the stem in Lyginodendron has been 

 compared to that of Osmunda and the Gymnosperms (Scott, 

 I.e., p. 314). 



Heterangium has a monostelic stem, which agrees closely 

 with that of Gleichenia, except for the secondary thickening. 

 Both Lyginodendron and Heterangium had leaves like those of 

 a typical Fern. Unfortunately practically nothing is known 

 about their sporangia. 



Of the more Cycad-like forms may be mentioned Cycado- 

 xylon and Medullosa. While the sporangia of these forms is 

 not certainly known, it is possible that they may have been het- 

 erosporous, or even seed-bearing. (For a full account of these 

 important forms, the reader is referred to Prof. Scott's work 

 (Chap. X, XI). 



During the past few years there have been found associated 

 with the Fern-like leaves of the "Neuropteris" and "Alethop- 

 teris" types, structures which appear to be real seeds, showing 

 that some, at least, of the Cycadofilices were seed-bearing 

 plants. For this reason it has been suggested that the name 

 Pteridospermeae be applied to the Cycadofilices (Grand 

 'Eury(i)). 



The peculiar genus Naeggerathia (Potonie (j). Fig. 158) 

 is one of the few spore-bearing fossils, which has been referred 

 to the Cycadofilices. 



EquisetinevE (Scott (i) ; Seward (i)) 



To this class are usually assigned two groups of fossil plants, 

 one belonging to the Equisetacese, and represented by the genus 

 Equisetites, which evidently was very close to the genus Equi- 

 setum, if not identical with it. The other group, the Calama- 

 riacese, differed in some respects from the living forms, and 

 there is much diversity of opinion about their real affinities. 

 The best known members of this order are the Calamiteae, 

 whose anatomical structure is well known. Cormack ( i ) has 

 made a comparison of the structure of these with Equisetum, 

 and comes to the conclusion that the type of structure is essen- 



