RHIZOCARPEjE 



37 



joranges. Fertilisation takes place within the drop of mucilage, which 

 len gradually disappears, and the impregnated megaspore lies on the 

 amp ground, to which it becomes attached by the rhizoids put out 

 om the prothallium until the first root of the embryo penetrates into 

 le soil. In Marsilea the processes are somewhat similar. The exces- 

 vely hard, almost stony, shell of 

 le sporocarp gives way slightly at 

 s ventral edge as it lies in water, 

 id the water penetrates into the 

 Lterior. This causes the suc- 

 jlent parenchymatous tissue in 

 ich compartment to swell up, 

 id splits the shell along the whole 

 f the ventral edge into two valves, 

 etween these valves the contents 

 re gradually forced, out; the com- 

 artments still remain closed, each 

 iclosing a sorus, and are attached 

 1 two rows to the cartilaginous 

 ashion or sorophore which ran 

 iong the ventral edge of the spo- 

 )carp,' and which now becomes 

 etached at one end, and ex- 

 osed in the form of a string 

 lany times longer than the sporo- 

 irp itself ; by the absorption of 

 ater it has increased enormously 

 1 size, to something like 200 

 mes its original dimensions, and 

 le sori are thus placed at a con- 

 derable distance from one an- 

 ther. Ultimately the walls of 

 le sori or original compartments 

 f the sporocarp disappear ; the 

 alls of the sporanges burst, both 

 inds of spore escape, and fertilisation is effected on the damp soil. 



All the species of both genera of Marsileacese are marsh or aquatic 

 erennial plants, mostly natives of the warmer temperate and tropical 

 Duntries. The number of species of Pilularia is small, of Marsilea 

 bout forty. The leaves of Marsilea, when growing in the air, display a 

 5nsitiveness to light, folding up in the evening and expanding in the 

 lorning, similar to those of many Leguminosse and other Flowering 



Fig. ig. — Sporocarp of Marsilea- salvatrix. A^ 

 transverse section. £, swollen and bursting, 

 shoiving sorophore (X2i). C, sporocarp (natural 

 size), -with sorophore fully extended, and sori 

 attached. ■ D^ section of sorus ( x 6) ; ids, indu- 

 sium ; fnik, microsporanges ; maki megaspo- 

 ranges. (After Hanstein.) 



