SPORE-PRODUCTION 



2 I 



are termed " sporophylls" but they do not differ in outline from" the 

 vegetative leaves (Fig. 2). The sori are disposed in a single linear series 

 on either side of the midrib of the pinna, or pinnule, being seated on 

 the secondary veins. The kidney-like outline which they present is 

 due to a membranous covering called the indusium, which is protective : 

 it is attached by a central stalk to a projecting cushion of tissue the 

 receptacle which is in close connection with the vein, while there is 



11. 



12. 



FIG. 5. 



Young stages of segmentation of the sporangium of Ne/>!i> odium fiiix-mns. (After Kny. ) 



a vascular extension from the vein into the receptacle. To the latter 

 are also attached the numerous sporangia, stalked capsules of lenticular 

 form, which are collectively overarched by the umbrella-like indusium. 

 Various stages of development of the sporangia may be found together 

 in the same sorus : those which are younger are smaller, and of pale 

 colour ; those which are mature are larger, and- are filled with numerous dark 

 brown spores : these showing through the more transparent wall give to the 

 ripe sporangium a deep chocolate colour. 



In order properly to understand the arrangement of the parts of the 

 sorus it must be cut in vertical section (Fig. 4) : it will then be seen 



