GROUP III. PTERIDOPHYTA : FILICIN^ ; HYDROPTERIDE^. 411 



aspect of the macrospore the perinium forms three (A. filiculoides 

 and caroliniana) or by segmentation nine (-4. pinnata and nilotica) 

 large spongy masses which constitute the so-called floats of the 

 spore : at the pointed apex of the spore, between these masses, the 

 perinium usually terminates in a tuft of delicate filaments. 



In the Marsileacese the spores become invested by a perinium, 

 secreted by the epiplasm, consisting of an inner layer made up of 

 prisms placed with their long axes perpendicular to the surface of 

 the spore, and of an outer layer which is homogeneous in the 

 case of the microspore ; but in the case of the macrospore it is 

 stratified, swells up enormously on being wetted, and gives the 

 cellulose-reaction. 



In all cases the spore has its own proper coats, the exospore 

 and the endospore, of the usual constitution. It contains a mass of 

 granular protoplasm, with a nucleus, and encloses numerous 

 starch-grains, oil-drops, and proteid granules. 



The dissemination of the spores is effected by somewhat peculiar 

 means. In Salvinia the spores remain enclosed in the sporangia, 

 but the sporangia break off from their stalks and float on the sur- 

 face of the water. In Azolla the indusium, as also the wall of the 

 free microsporangia, slowly decays, and the massulae of micro- 

 spores escape ; but the macrospore remains covered in its upper 

 end by the wall of the sporangium and by the indusium : in those 

 species in which glochidia are present, the massulae become hooked 

 on to the projecting filaments of the macrospores. In the Mar- 

 sileaceae the hard sporocarp must first of all be opened ; this is 

 effected by the mucilaginous walls of the internal tissue of the 

 mature sporocarp, which, when the sporocarp is moistened, absorb 

 water and swell up considerably. In Pilularia the tension thus 

 produced causes the wall of the sporocarp to split into 2-4 valves 

 at the apex, and through this opening the mucilage escapes carry- 

 ing with it the spores. In Marsilea there is a well denned strand 

 of swelling tissue extending along the dorsal and ventral margins of 

 the sporocarp and forming a continuous ring with which is con- 

 nected the tissue enclosing the chambers containing the sori : 

 when water gains entrance to the mature sporocarp, this tissue 

 swells and, first of all, causes the rupture of the wall of the 

 sporocarp along the ventral suture ; the ring continues to swell 

 and drags out with it the chambers and the contained sori till 

 they lie freely in the water ; it is estimated that the ring swells 

 up to about 200 times its original size ; the delicate tissue sur- 



