RHIZOCARPE.E. 



393 



leaf-stalk. These fruit-stalks may be simple, bearing only one sporocarp, or forked 

 and bearing several ; those situated on the leaf-stalks are mostly divided, while the 

 basal ones bear only one sporocarp. This peculiarity finds its analogue in the 

 Ophioglossaceae ; the fruit-stalks of Marsilea may be compared with the 'fertile 

 segments ' of the leaves in that class. The sporocarps of Salvinia and Marsilea are 

 therefore always of foliar origin ; in Pilularia they are shortly-stalked and axillary, 

 or grow on the ventral side of the insertion of the leaf, and their fibro-vascular 

 bundles spring from the axils of the foliar bundles. In other respects the struc- 

 ture of the sporocarps shows material differences in the three genera. In Salvinia 

 (Fig. 294, B) they contain a single spacious cavity ; at its bottom a stalk arises, 

 which swells up into a spherical form in the centre of the cavity, and contains a 



Pig. 293 (T.— Lonj;ituciinaI section of the young 

 primary root of the embryo of Afarsilca sal- 

 vatrix; ivs the apical cc\],7v/t',7vh", tvh'" the 

 still simple root -cap; jr.j'the last segments of the 

 substance of the root ; i i intercellular spaces 



Fig. 293 /'.—Longitudinal section of a somewhat older primary root of Marsilea salvatrix ; ws apical cell ; ivhl + w/z2 the first, 

 ■whSJ^wM the second, ■wli'a the third layer of the root-cap ; each layer now consists of two divisions; xy the youngest segments 

 of the substance of the root ; epidermis ; ^--y" fibro-vascular bundles ; h the part of the root-cap which extends furthest back. 



prolongation of the axial fibro-vascular bundle of the tooth of the leaf, the termi- 

 nation of which is the sporocarp ; on this spherical swelling are formed a number 

 of sporangia, which produce exclusively macrospores or microspores within the same 

 sporocarp. In Salvinia therefore the diff"erence of sexes of the spores reaches back 

 to the sporocarps themselves. In Pilularia the cavity of the sporocarp is divided 

 into vertical compartments (/. e. parallel to the axis) ; in P. minuta it is bilocular, 

 in P. americana trilocular, in P. glohtdifera quadrilocular ; each chamber bears on its 

 peripheral side a cushion running from the base to the apex of the sporocarp 

 and projecting inwards, behind which runs a fibro-vascular bundle. On this 

 cushion a number of sporangia are formed, the lower of which produce macro- 

 spores, the upper microspores. A cushion of this kind bearing sporangia n.ay be 



