FERNS— FRUCTIFICATIONS 277 



or not, and will begin with one in which very definite 

 confluent synangia were present. 



This fructification, to which the generic name of 

 Ptychocarpus, Weiss, has been given, was borne on 

 leaves of the Pecopteris form ; the species described is 

 P. unitus, Brongn., from the French Coal-measures. 



The fructification of Ptychocarpus unitus was borne 

 on the ordinary frond. The sporangia are grouped 

 six to eight together, in circular sori ; the sporangia of 

 each sorus or synangium are united laterally among 

 themselves, and are at the same time adherent to the 

 central receptacle, which rises up in the middle of the 

 group (see Fig. 108, C). The synangia are ranged 

 in one or two series, along each side of the median 

 nerve of the fertile segment (Fig. 108, A). They are 

 prominent and shortly-stalked bodies (Fig. 108, B), 

 which often became detached entire from the surface 

 of the pinnule. As shown by the transverse section, 

 each sporangium has a wall, or rather perhaps a 

 tapetum, of its own, but the whole sorus is embedded 

 in a delicate tissue, which is quite continuous round 

 the periphery (Fig. 108, C). The receptacle is 

 traversed by a vascular strand. The spores in each 

 sporangium are numerous and very small, measuring 

 only from 18 to 20 fi in diameter. There is no trace 

 of an annulus. M. Renault, to whom our detailed 

 knowledge of this fructification is due, conjectured, 

 with much probability, that each sporangium discharged 

 its spores through an apical pore. In general characters, 

 the Ptychocarpus fructification approaches most nearly 

 to that of the recent genus Kaulfussia, in which 

 the synangia are also circular, but there are many 



