Spores alongwith cytoplasm of degenerating tapetal cells form small units called massulae .
Azolla
Azolla is also known as mosquito fern or mosquito net .They are found on the surface of permanent pools . Azolla imparts characteristic reddish colour to the pond .
Sporophyte is made up of branched rhizome , adventitious root and leaves .The mature rhizome has ectopholic siphonostele . leaves are minutes ( up to .5 m ) . They grow in two alternating rows on the dorsal surface of rhizome . Each leaf is divided into two equal lobes -
1. Aerial lobe - upper , green , thick , photosynthetic , obliquely placed , touches water only on the edges , has large cavity containing anabaena azollae .
2. Submerged lobe - lower , thin , colourless , absorbs water .
Upper epidermis of leaf is covered a tuft of hair which traps air and protects leaves from wetting .
Vegetative reproduction occurs by fragmentation . Two types of sporocarps - microsporocarps and megasporocarps are fund in azolla . Each sporocarp is capable of bearing either microsporania or macrosporangia but during the development they get either of them . Megasporangium is always the first to be formed . If megasporangium degenerates then microsorangium is formed . Sporocarps are borne on the fertile lobe of lowermost leaf of a lateral branch . True Indusium ( from stalk ) is present and surrounds the sporangium completely except opening . Azolla is heterosporous .
Large megspore ( 1 ) with surrounding degenerating cytoplasm of other megaspores ( 19 ) form a honeycomb like float corpuscle or massulae . It serves as swimming apparatus and provides buoyancy to the megaspore .
Microspores and cytoplasm of degenerating tapetal cells form float corpuscles or massulae . Each massulae has peripherally situated cytoplasmic strands called glochidia . This massulae attaches to the rugged surface of the megaspore with the help of glochidia . Both the mega and microsporocarps sink to the bottom of the pond . Massulae are set free after the death and decay of sporocarp wall .
Salvinia
Salvinia are free floating aquatic ferns . They are found in still waters of pond and lake . They lack roots . They have hairy branched rhizome .The node bears leaves and branches . Salvinia shows dimorphism of leaves . They have tow types of leaves - floating and submerged leaves . Upper epidermis of floating leaves have hair to trap air and to prevent from wetting . Submerged leaves are finely divided , boat shaped and act as balancers .
Salvinia is heretosporous water fern . Each sporocarp represents a sorus . All sporocarps are strictly monosporangiates ie. they bear either microsporangia or macrosorangia . All other features of sporophytes and gamatophytes are similar to azolla .