PTERIDOPHYTES 



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 

 son (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 

 in 



410 409 



microspores * FlGS ' 408-410. Marsilea: 408, inside of one of 

 ' the " valves " of the sporocarp, showing the system: 



while in each megaspo- O f veins, the short branches supplying the" sori; 



rangium only one mega- 49> section through a sporocarp, showing the two 



spore matures, as in the r s of sori beginning to develop (terminal cell in each 



. ' . is a young megasporangium) ; 410, section through 



oalViniaceae. ineson are a young sorus, showing a developing megasporangium 



attached to a tissue which (cutting off tapetal cells) above, and a microspo- 



swells remarkably upon y angium ! m ' tial . a PP earin s on each side below; the 



investing indusium is evident. After JOHNSON. 

 exposure to water, dragging 



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- 

 tending 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 



