PTERIDOPIIYTKS 



177 



that is, by the fusion of 

 lateral branches (p. 152). 

 The sporocarp seems to be 

 a modified leaf blade or 

 blades enclosing a group of 

 sori (fig. 408). In Marsilea 

 the sporocarp is somewhat 

 bean-shaped, each sorus 

 being in a cavity that ex- 

 tends from the ventral side 

 towards the dorsal (fig. 

 409). Lining each cavity 

 is a delicate indusium com- 

 pletely investing the sorus, 

 which contains both micro- 

 sporangia and megaspo- 

 rangia (fig. 410). In the 

 microsporangia all the 

 mother cells function in 

 producing microspores ; 

 while in each megaspo- 

 rangium only one mega- 

 spore matures, as in the 

 Salviniaceae. The sori are 

 attached to a tissue which 

 swells remarkably upon 

 exposure to water, dragging 



410 409 



Figs. 408-410. — Marsilea: 408, inside of one of 

 the " valves " of the sporocarp, showing the system 

 of veins, the short branches supplying the sori; 

 409, section through a sporocarp, showing the two 

 rows of sori beginning to develop (terminal cell in each 

 is a young megasporangium); 410, section through 

 a young sorus, showing a developing megasporangium 

 (cutting off tapetal cells) above, and a microspo- 

 rangium initial appearing on each side below; the 

 investing indusium is evident. — After JOHNSON. 



the sori out, from the 

 ventral side of the sporo- 

 carp, attached to a muci- 

 laginous ring formed of 

 the swollen tissue (fig. 

 411). In Pilularia the 

 sporocarp is globular, 

 four soral cavities ex- 

 truding from the base 



towards the apex, the 

 Fig. 411. — Marsilea: the swelling mucilaginous ring . ... 



dragging out sori (indusia enveloping sporangia) from microsporangia being 



the sporocarp. above and the megaspo- 



C. B. & C, BOTANY — 12 



