OF FILICALES 



In the Ophioglossales the structure of the shoot at large is open to 

 various interpretations ; but without entering here into questions which 

 will be taken up in detail later it will suffice to mention that in 

 Helminthostachys there are sporangiophores which are broadly similar 

 in outline to those of Equisituin, but they are borne in irregularly 

 disposed bands on the lateral margins of the fertile spike (Fig. 83). 



It may at first sight seem difficult to bring the very varied disposition 

 of the sporangia upon the enlarged sporophyll in modern Ferns into line 

 with these examples of spore- 

 bearing bodies in smaller-leaved 

 types. But it is to be remem- 

 bered that in Palaeozoic Ferns 

 definite sori were common ; 

 they were as a rule of circular 

 form, and all their sporangia 

 were produced simultaneously. 

 The wide-extended sori, such 

 as are frequently found among 

 the Folypodiaceae, were pro- 

 bably of relatively late and 

 secondary origin, by extension 

 of the sori of the circumscribed 

 type. Now, a circular sorus, 

 with relatively few sporangia 

 formed simultaneously and 

 borne upon a more or less pro- 

 jecting receptacle, into which, 

 as may often be seen, a vascular 

 supply extends, differs in no 

 essential from such bodies as 

 we have been considering. A 

 sorus of this simple type is 

 seen, for instance, in Kaiilfussia, 

 which is closely similar to that 

 of the Palaeozoic Fern, Ptycho- 

 carpus niiitits (Fig. 84). It has 

 been seen that spore-bearing 

 bodies may be borne directly 

 on the axis or on the appen- 

 dages ; the latter is the case in the Ferns, the chief difference between 

 them and the strobiloid forms being that the appendages here are large 

 and the sori, or sporangiophores, very numerous. Regarded in this light, 

 the Fern-type is not a thing distinct or apart ; the difference from other 

 types is mainly one of the degree of development of the sporophyll which 

 bears the sori. 



FIG. 84. 



PtycJiocarpiis itnitus. Fructification. A, part of a (Vi nl<- 

 pinnule (lower surface), showing numerous synangia. /', 

 synangia in side view. (A and B X about 6.) (After < Irani!' 

 Eury.) C, a synangium in section parallel to the surface of 

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

 receptacle; />, its parenchyma ; < , tapetum ; d, spores ; f, f, 

 common envelope of synangium. X about 60. (After 

 Renault.) From Scott's .Stmiu's in Fossil ttotany. 



