520 



FILICALKS 



as a slight modification of this, by localisation of the sclerotic thickening 

 so as to form a hoop-like band, while the remaining walls are thin. 



It is thus seen that the sporangia of the living Marattiaceae conform 

 essentially to a single type : but that that type is less definite in its 

 detailed characters than is the case in other Ferns : and this goes along 



with their larger size, and the 

 high output of spores, which is 

 its natural concomitant. For 

 on computation in round num- 

 bers, the sum of the spores 

 potentially present in a spor- 

 angium of Angiopteris is about 

 1450: of Danaca about 1750: 

 of Marat tia about 2500 : and 

 of Kaulfussia about 7850. It 

 is thus seen that the synangial 

 forms have the largest number. 

 This, with various other con- 

 siderations, will have weight 

 in the discussion whether the 

 state with synangia or that with 

 separate sporangia is probably 

 the more primitive. 



Passing now to the fossil 

 Ferns having fructifications 

 which may be ascribed to a 

 Marattiaceous affinity, many of 

 them had foliage of the Pecop- 

 terid-type (Fig. 287), though this 

 in itself cannot be held as any 

 clear indication of relationship : 

 it is the soral structure which is 

 distinctive. A few of the best 

 known examples will be de- 

 scribed, with a view to their 

 comparison with the fructifica- 

 tions of the living Marattiaceae. 



One of the most striking is Ptychocarpus (Pecopteris) unita : ] here, on the 

 lower surface of the pinnules of a Pecopterid leaf, the sori are disposed 

 on either side of the midrib : each is a solid synangium, composed of 

 about seven sporangia united upon a common receptacle. Each synangium 

 is attached by a short and narrow pedicel, so that it may be removed 

 bodily, and the synangia are frequently found lying free. The form is 

 that of a truncated cone, with a slight terminal dimple. The sporangia 



'Renault, h'assin Hotiillt-r d' Anlitn, li., p. 9. 



A 



FIG. 288 



Ptychocarpns unitus. Fructification. A, part of a fertile 



- . . 



the leaf, showing seven confluent sporangia, a, bundle of 

 receptacle ; b, its parenchyma ; c, tapetum ; d, spores ; e,f, 

 common envelope of synangium. .ilmut DO. (After 



Renault.) From Scott's Studies in /v>.v.v/7 1'mtany. 



