FERNS— FRUCTIFICATIONS 279 



The fructification of Ptychocarpus unitus is, however, 

 a good example of a typical Marattiaceous synan- 

 gium, and affords strong evidence as to the affinities of 

 the plant. 1 



Mr. Watson has recently described, under the name 

 Cyathotrachus altus, a synangium of Lower Coal- 

 measure age, differing from Ptychocarpus in its taller 

 shape, in having a cup-like central depression, and in 

 the presence of tracheides at the base of the sporangia ; 

 in the two latter characters it approaches Kaulfussia. 

 The specimens were isolated, but were associated with 

 a pinnule, probably of a Pecopteris. There is a pre- 

 sumption in favour of Marattiaceous affinities, but the 

 same doubts apply here as in other cases of the kind. 2 



The important genus Asterotheca resembles Ptycho- 

 carpus* in the fact that in each sorus the sporangia 

 are grouped in a ring around the receptacle, but the 

 receptacle is short, the sporangia are usually from three 

 to six only in number, and are less closely united 

 to one another. The sori are ranged on the under 

 surface of the pinnule in two rows, one row on each 

 side of the median nerve (see Fig. 109, A). The 

 individual sporangia are ovoid in shape, and there 

 is reason to believe that when ripe they separated from 

 each other, bending outwards from the central receptacle, 

 and dehiscing by a longitudinal opening on the inner 



1 See Renault, Bassin houiller el permien d'Autun et d'Epinac, 

 Part ii. p. 9. 



2 D. M. S. Watson, "On a ' Fern ' Synangium from the Lower Coal- 

 measures of Shore, Lancashire, "Journal R. Microscop. Soc. 1906, Part i. 



3 These genera are founded solely on the fructification, and are thus 

 likely to represent more natural groups than those based on the form and 

 venation of the frond. See Stur, "Zur Morphologie und Systematik der 

 Culm- und Carbonfarne,'' K. Akad. d. Wiss. Vienna, 1883. 



