THE FERNS 



133 



groups of sporogenous cells are much less definite than 

 in Ophioglossum, and do not have a separate opening 

 for each ; still it is quite conceivable that the simple 

 sporangia of Ophioglos- 

 sum may have originated 

 from structures not unlike 

 the groups of sporogenous 

 cells found in the Antho- 

 cerotacese. 



In the ferns, as in the 

 mosses, each sporogenous 

 cell gives rise to four 

 spores, which develop in 

 an absolutely similar way, 

 and offer another striking 

 proof of the close rela- 

 tionships of the two 

 groups. 



If we admit that Ophio- 

 glossum shows the most 

 primitive type of spo- 

 rangium among the ferns, 

 we may say that passing 

 from this type to that 

 found in the most special- 

 ized ferns, the so-called 

 " Leptosporangiatse," we 

 encounter an almost perfect series of intermediate forms 

 leading up to the exceedingly specialized sporangium 

 of the latter, and this series may be assumed to rep- 

 resent the evolution of the sporangium of the lepto- 

 sporangiate ferns from the simpler type found in 



Fig. 34 (Eusporangiate Ferns). — A, 

 sporophyte joi an adder-tongue fern 

 {Ophioglossum vulgatum); up. the 

 sporangial spike; B, longitudinal 

 section of the sporangial spike 

 of another species (0. pendulum), 

 showing the cavities containing the 

 spores ; C, cross-section of the spo- 

 rangial spike of 0. pendulum; D, 

 separate sporangia of Botrychium ; 

 E, leaflet of Marattia, showing the 

 synangia, or coherent sporangia; F, 

 a single synangium cut to show the 

 separate sporangial cavities ; G, 

 Angiopteris, one of the Marattiacese 

 with nearly separate sporangia, sp. 



