512 



FILICALES 



B 







SPORE-PRODUCING MEMBERS. 



The sorus of the modern Marattiaceae is strictly circumscribed, and 

 has no definite indusium : it is true that certain hairs round its periphery 

 in Angiopteris have been thus described, but they hardly deserve such 

 recognition (Fig. 283 B, D): also in Danaea the tissue of the leaf grows up 

 between and partly envelops the sori where they are in close juxtaposition, 

 and the growth has been called an indusium, but this use of the term 

 is open to question (Fig. 283 K). The sori are all constructed on a plan 

 which may be described as radiate, and uniseriate, for a single series of 

 sporangia are disposed in a radiate fashion round a central attachment. 

 When the sorus is circular, as in Kaitlfussia, the attachment is at a central 



point : when elongated, as 

 in Danaea, the attach- 

 ment is linear. All the 

 sporangia of a sorus ori- 

 ginate simultaneously, a 

 character which is general 

 for the Simplices. The 

 sporangia themselves may 

 be separate, or united into 

 synangia : they are massive, 

 with a broad base of in- 

 sertion, and each produces 

 a large output of spores. 

 The dehiscence is in all 

 cases by a slit or pore, 

 in a median position at 

 the distal end, or on the 

 oblique inner face of each 



sporangium : there may be differences of the opening mechanism, but the 

 plan of dehiscence is the same in them all. 



The structure of the mature sori of the five genera is illustrated in 

 Fig. 283. Figs. A and E represent the sori of Angiopteris and ^\Iarattia : 

 the plan of them is clearly the same, the difference being that in the 

 former the sporangia are separate, in the latter they are fused into a 

 synangium, which is of firm, almost woody texture. Each sporangium in 

 either case opens by a slit on the oblique inner face. The question 

 will be considered later whether the synangial condition or that with 

 separate sporangia is probably the more primitive : meanwhile, as regards 

 the general character of the sorus, these genera may be regarded as central 

 types in the family, while the rest of the genera are probably derivative. 

 Thus an elongation of the sorus of Angiopteris, so that it occupies a 

 considerable length of each vein, would give the condition seen in 

 Archangiopteris (Fig. 283 c, D). It is probable that this is the correct 



FIG. 282. 



A, B, Scolecopteris elegans, Zenker, from the lower Permian. 

 A= transverse section of a fertile pinnule enlarged (after Zenker). 

 B = Scolecopteris polymorpha, Brongn, from the Stephanian, longi- 

 tudinal section of a fertile pinnule enlarged (after Grand' Eury). 

 C, D, E, Asterotheca. C = Asterotheca Miltoni, Astis, from the 

 Westphalian : fertile pinnules. X 2. D = synangium of Asterotheca. 

 X about 6. E = longitudinal section of a pinnule of Asterotheca, 

 traversing three synangia, enlarged. (After Grand' Eury, from 

 Zeiller's Palaebotanique.) 



