SPORE-PRODUCTION 21 
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 
Fic. 5. 
Young stages of segmentation of the sporangium of Nephrodium Filix-mas. (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 sgoves:: ‘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 
