146 



MANUAL OF BOTANY 



contain both micro- and niacrosporangia. In Marsilea there is 

 in each a single row of the latter in the middle, and a double 

 row of the former on each side of it. In Pilularia the arrange- 

 ment is not so definite. 



The sporocarp is 

 made to rupture by the 

 mucilaginous character of 

 the internal tissue, which 

 absorbs water and causes 

 the wall of the sporo- 

 carp to split. In Pilularia 

 the rupture begins at the 

 apex, in Marsilea it takes 

 place along the side. In 

 the sporocarp of the latter 

 is a band or ring of mu- 



FiG. 904. 



Fig. 90.5. 



Fig. 904. Transverse section 

 of the sporocarp of Pilu- 

 laria glohulifera. After 

 Henfrev. 



cilaginous tissue, to which 

 the walls of the chambers 

 containing the sori are at- 

 tached. When the sporo- 

 carp ruptures hy the swell- 

 ing of this ring, the latter 

 protrudes through the 

 opening, and still swelling 

 drags out with it the sori 

 in a kmd of string or chain 

 {fig. 905, B c). AYhen free 

 from the sporocarp the 

 walls of the sori-chambers 

 and those of the sporangia disintegrate, setting free the spores. 



The spores in this group of plants are characteristic. Instead 

 of possessing onl}' two walls and lying free in the sporangia, as 



Fig. 905. Marsilea salvatrix. A. A sporocarp 

 (natural size). B. A sijorocarp which has 

 burst its water and is protruding its gelati- 

 noiis ring. After Hanstein. c. Tiie ring 

 ruptured and extended, showing the sepa- 

 rated sori, sr. D. A sorus showing macro- 

 sporangia and microsporangia. E. A sorus 

 from a ripe sporocarp. After Sachs. 



