XXIIlJ 



MORPHOLOGY 



179 



Fig. 461. Successive types of juvenile leaves 

 of Marsilea. (After Braun.) 



a more highly branched leaf of the type of Anejiiia through 6, 4, and 2 

 lobes, and finally to the unbranched type of Pilularia, which in its adult 

 state simply repeats the cotyledonary stage. Marsilea, like Pilularia, bears 

 a sporocarp on each leaf, sometimes several, or even many as in M. polycarpa. 

 Their relation to the stipe is lateral. These fruiting bodies are hard and 

 woody when ripe, with a hairy surface, and each is borne upon a stalk of 

 variable length which sometimes branches, as in M. qiiadrifolia (Fig. 459). 

 The shoot of Marsilea is more or less frequently branched, and the branches 

 are extra-axillary, arising on the flanks of the main rhizome. This again 

 suggests a dichopodial origin, as in Pilularia. Though the genus is typically 

 semi-aquatic it includes xerophytic species, such as the Australian M. hirsuta, 

 which retains its vitality under long drought, It has, like so many Australian 

 xerophytes, an underground rhizome with tuberous buds which persist after 

 the rest of the plant dies, and germinate as soon as the conditions are 

 favourable, producing fertile leaves. 



The newly discovered Regnellidijiin (Lindman, Ark. f. Bot. iii, 1904), 

 from South America, is represented by one species, R. diphyllum, so called 

 from the distinctive fact that it has constantly only two leaf-lobes. The 

 veins are repeatedly dichotomous, and are united as in Marsilea by marginal 

 loops. The veins of the fruit fork also, and the shanks of the same vein may 

 unite at the margin, as well as intramarginall)': but the primary veins 

 remain distinct and separate. The new genus thus appears to take a natural 

 place between Marsilea and Pilularia. 



