XI 



LEPTOSPORANGIAT^ HETEROSPOREJE 



431 



internodes. At the nodes are borne the various appendages of 

 tlie stem, and the elongated internodes are, except for occa- 

 sional roots, quite destitute of appendages. Leaves and 

 branches arise from the nodes, and in Marsilia are much 

 crov^ded. The plants are aquatic or amphibious, and the habit 

 of the plant is very different, especially in Marsilia, as it grows 

 completely submerged, or partially or entirely out of water. 

 Some species, like M. vestita, which grow where there is a 



Fig. 253. — Marsilia vestita. A, Vertical longitudinal section of the stem apex, X8o; 

 L, leaves; st, stem apex; r, roots; B, the stem apex, X450; C, horizontal section of 

 very young leaf, X450; D, similar section of an older one, X4S0; E, cross-section 

 of petiole, X8o. 



marked dry season, grow^ in shallow ponds or pools, which dry 

 up as the end of the growing period approaches, and the ripen- 

 ing of the sporocarps takes place after the water has evaporated. 

 In the first case the petioles are extremely long and weak, and 

 the leaf-segments float upon the surface. In the other case the 

 petioles are much shorter and stouter, and the leaves are borne 

 upright. The young leaves are circinate, as in the ordinary 

 Ferns, and in Pilularia retain the same structure as the coty- 



