no 



DRYOPTEROID FERNS 



[CH. 



which the drawing was made, has shown that he was in error in attributing 

 a fully cup-shaped indusium to Peranema. The structure which he described 

 as the "laggard portion" of the indusium in Fig. 653 is really a young 

 sporangium, and the indusium is not continuous all round the receptacle. 

 This fact is demonstrated for the young sorus by Fig. 654, A, in which the 

 section follows the course of a vein, and traverses the margin : the hemi- 

 spherical receptacle thus cut in a median plane is seen overarched b}^ the 



Fig. 654. A, i5 = sections of young sori oi Peranenia from prepara- 

 tions made by Dr Davie. ^ = vertical section in plane cutting the 

 leaf-margin. j5 = vertical section in plane parallel to the leaf-margin. 

 C = a section of a young sorus o{ Dryopteris filix-inas, in similar plane 

 to A, for comparison. {A, j9 x 165. C x 63.) C is rather older than 

 A and B, and it shows signs of a basipetal sequence of sporangia. 

 A' = receptacle. « = indusium. ^1^ = vascular bundle. 



indusium, which has a free lip, and there is no corresponding lip on the 

 marginal side. The structure is made still clearer by Fig. 654, B, which 

 represents a sorus similar to A, but cut in a plane at right-angles to it, and 

 hitting the vein transversely. The indusium appears then as a close-fitting 

 arch, the margins of which right and left are free, while the receptacle 

 appears in this plane of section detached from it, as well as from the leaf- 

 surface. But as the sorus develops the margins of the indusium grow 

 forwards, coming into contact, and even folding inwards so as to form the 

 narrow slit above described. These details are important for comparison 



