210 MORPHOLOGY. 



Salvinia consists of an upper, under, and central layer of cells, 

 which are somewhat removed from each other, the space between 

 them being divided into large air-cavities by vertical septa, the cells 

 of which exhibit undulating walls. The upper layer consists of 

 polygonal cells, which have intercellular passages (stomates) between 

 them, opening into the air-cavities beneath. The upper surface is 

 also studded with tufts of hairs, composed of cells in a moniliform 

 arrangement ; the lower surface of the leaves, the stem and the 

 radical fibres, are covered with hairs of a somewhat different kind, 

 composed of cylindrical cells arranged into filaments, the last cell 

 of which is apiculate, and contains some dark- coloured substance. 

 The blade of the leaf of Marsilea consists (according to Bischoff) of 

 parenchyma, traversed by forked, branching vascular bundles, and 

 covered by an epidermis furnished with stomates on both (?) sur- 

 faces, and having the lateral walls of its cells serpentine. The 

 coriaceous coat of the fruit in Marsilea and Pilularia is composed 

 of from three to five layers of cells, elongated vertically to the sur- 

 face, of various colours, unequal in width, but all with thick walls ; 

 in Pilularia this is immediately invested on the inner side by 

 a brownish parenchyma, composed of small cells, and forming air- 

 cavities in the places between the fruit and the septum ; next to 

 this (and exclusively in Marsilea) by a layer of gelatinous cells, 

 which in Marsilea exclusively form the transverse septa, while in 

 Pilularia a double layer of thick, brown, minute-celled parenchyma 

 also traverses these. The longitudinal septum, also, in Marsilea 

 consists of gelatinous parenchyma. At its upper free border, from 

 the base of the fruit outward, runs a vascular bundle, which sends 

 off as many main branches as there are transverse septa, and these 

 main branches, divided by bifurcation about the middle and then at 

 the very bottom, form a complicated anastomosis. Of the outermost 

 of the very minute cells of the coriaceous coat of the seed-bud in 

 Pilularia) those situated in the half lying next the nucleus are 

 somewhat more elongated, so that they form a collar round the 

 seed-bud. In Marsilea, the exterior cells are elongated perpendi- 

 cularly to the surface, yellow, and pass immediately into the cellular 

 integument. 



The history of development of the various masses of gelatinous cellular 

 tissue, which appear so peculiar in many respects, still remains an espe^ 

 cial desideratum. The cellular cord, bearing little sacs, which in Mar- 

 silea lies in the fruit, not more than two or three lines long, expands after 

 the dehiscence of the fruit, through absorption of moisture, to the enor- 

 mous size of a round filament from one to two lines thick, and four to five 

 inches long, the volume exceeding twenty or thirty times that of the 

 whole fruit. The layer of gelatinous cells, which enclose the seed-buds 

 in Marsilea and Pilularia, is also peculiar, and undergoes continual 

 change during the development, from the action of the water absorbed. 

 Many other specialities are to be found in Bischoff. * 



* Kryptogamische Gewaehse, p. 72, et seq. 



