RHIZOCARPEsE 



35 



on the procumbent stem. According to Juranyi, each sporocarp is the 

 result of the coalescence of two segments of bifid leaves. The wall of 

 the sporocarp is very thick and hard, and consists of several layers of 

 cells forming a sclerenchymatous tissue. It is divided by vertical walls 

 into compartments, varying from two to four in the different species. 

 Each compartment has, at least in its young state, an opening at the 

 apex, and is therefore not of endogenous origin, but rather a depression 

 in the surface. In each compartment there is, on the side which forms 

 its outside wall, a cushion-like placenta, formed from superficial cells, 

 and resting on a ' vascular ' bundle. To this placenta are attached a 

 number of stalked sporanges of both kinds, constituting a sorus ; the 

 megasporanges are chiefly below, 

 and the microsporanges above. 

 The remainder of each compart- 

 ment is occupied by a delicate 

 thin-walled parenchyme. When 

 mature the sporocarp splits from 

 the apex downwards into as many 

 valves as it has compartments ; 

 and each sporange dehisces by 

 the expansion of the gelatinous 

 mass resulting from the dissolu- 

 tion of the tapetal cells. 



The sporocarps of Marsilea 

 are capsules with somewhat the 

 shape of a bean, a longer or 

 shorter pedicel,^ and a very hard 

 sclerenchymatous wall. They 

 spring, usually in clusters, from 

 the petiole of an ordinary leaf. 

 The pedicel runs along the dorsal edge of the sporocarp, and gives 

 off lateral veins right and left which branch dichotomously and run to 

 the ventral edge. The ripe sporocarp has a bilaterally symmetrical 

 structure, and is divided by transverse walls into two rows of compart- 

 ments, each of which has, when young, a narrow opening on the ventral 

 side. Each compartment contains a single sorus, consisting of a few 

 megasporanges in the centre, with a larger number of microsporanges on 

 each side. As in Pilularia, a large portion of the cavity of each compart- 

 ment is occupied by a succulent parenchyme. 



The development of the sporanges commences, in both genera, with 

 the swelling up of some of the epidermal cells of the part which 

 ultimately becomes the placenta. These cells divide several times 



FIG. 18. Transverse section of sporocarp of Pilu- 

 laria. globulifera. mi, microsporanges; ma, 

 megasporanges ; e, wall of sporocarp ; g, paren- 

 chyme. (After Goebel, magnified.) 



