RHIZOCARPE^: 



37 



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

 then gradually disappears, and the impregnated megaspore lies on the 

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

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

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

 sively hard, almost stony, shell of 

 the sporocarp gives way slightly at 

 its ventral edge as it lies in water, 

 and the water penetrates into the 

 interior. This causes the suc- 

 culent parenchymatous tissue in 

 each compartment to swell up, 

 and splits the shell along the whole 

 of the ventral edge into two valves. 

 Between these valves the contents 

 are gradually forced out; the com- 

 partments still remain closed, each 

 enclosing a sorus, and are attached 

 in two rows to the cartilaginous 

 cushion or sorophore which ran 

 along the ventral edge of the spo- 

 rocarp, and which now becomes 

 detached at one end, and ex- 

 posed in the form of a string 

 many times longer than the sporo- 

 carp itself ; by the absorption of 

 water it has increased enormously 

 in size, to something like 200 

 times its original dimensions, and 

 the sori are thus placed at a con- 

 siderable distance from one an- 

 other. Ultimately the walls of 

 the sori or original compartments 

 of the sporocarp disappear ; the 

 walls of the sporanges burst, both 

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



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

 perennial plants, mostly natives of the warmer temperate and tropical 

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

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

 sensitiveness to light, folding up in the evening and expanding in the 

 morning, similar to those of many Leguminosse and other Flowering 



FIG. 19. Sporocarp of Marsilea salvatrix. A, 

 transverse section. B, swollen and bursting, 

 showing sorophore ( x 2$). C, sporocarp (natural 

 size), with sorophore fully extended, and sori 

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

 sium ; mik, microsporanges ; mak, megaspo- 

 ranges. (After Hanstein.) 



