204 



GLEICHENIACEAE 



[CH. 



The extreme state for this Family is seen in G. pectinata, in which the 

 number of sporangia in a sorus may frequently be lo or 12 (Fig. 488). 

 These are densely crowded together on the central receptacle. Where the 

 number of the sporangia in the sorus is more than 5, as in G. linearis 

 and pectinata, single sporangia may be displaced perhaps by lateral 

 pressure, so that their dehiscence is not strictly radial to the centre of the 

 sorus, but oblique: and this irregularity naturally appears where the centre 

 of the sorus is occupied by one or more sporangia. In such examples we 



Fig. 486. Pinnule of Glcichenia linearis Fig. 487. A single sorus of Gleichenia linearis 



showing the venation, and mature sori. on a larger scale, showing the disposition of 



Some of the sporangia are seen to have the sporangia, several of which have opened 



dehisced. (Enlarged. Drawn by Mr by a median slit. (Drawn by Mr Maxwell.) 

 Maxwell.) 



see the extreme development of the Gleicheniaceous sorus. In none of them 

 is an indusium present, though a dense flocculent growth of hairs may 

 surround the sorus, especially in the xerophytic types. It will be realised 

 that by such species as those last named the gap is bridged between two 

 well-marked types of sorus. On the one hand is the type of the Marattiaceae, 

 which is shared by most of the Gleicheniaceae, where a single series of 

 sporangia surrounds the periphery of the low receptacle: on the other is the 

 type of the Cyatheaceae, and other Gradatae, where the receptacle is more 



