i8o 



MARSILEACEAE 



[CH. 



Anatomy 

 The anatomy of the Marsileaceae is that usual in relatively primitive Ferns 

 with creeping rhizomes. In Marsilea the stem is traversed by a normal 

 solenostele, with inner phloem and endodermis, while in plants grown on 

 solid ground the central pith is usually sclerotic. The undivided leaf-trace 

 separates a sector of the ring in the customary manner. The cortex may 

 be differentiated as an inner starchy storage tissue, separated by a thin 

 sclerotic band from an outer tissue containing large radiating lacunae with 

 thin parenchymatous septa, — a peculiarity commonly seen in aquatic plants. 

 The structure of the rhizome is similar in Pilnlaria, but on a smaller scale, 

 and the inner endodermis may be absent. The petiolar trace is of the same 

 type as that of Anemia (compare Chapter XXII, Fig. lo), but it is reduced in 

 size and complexity in Marsilea and still more so in Pilularia. The vas- 

 cular supply to the stalk of the sporocarp comes off after the manner of the 

 pinna-trace of the Schizaeaceae, viz., by marginal abstriction, a point of 

 importance as bearing on the question of its morphology (Fig. 462). The 



'■cT^xp^? 



Fig. 462. Alarsileapolycarpa. Transverse section of the petiole, 

 below the insertion of the lowest sporocarp, and showing 

 on the right the sporocarp-trace, given off marginally, as in 

 the sterile pinnae. (After Miss Allison.) ( x 175.) 



petiolar trace is marked off by endodermis from the parenchyma outside, 

 which is again differentiated into an inner coherent tissue with tannin-sacs, 

 and an outer lacunar tissue with peripheral epidermis, and sclerotic tissue 

 between. The roots are diarch, with a conical apical cell, and regular lacunar 

 cortex. In Pilularia peculiar spirally coiled cells occupy the lacunae, acting 

 probably as mechanical props, as in the Nymphaeaceae, 



The chief interest in the sporophyte of the Marsileaceae lies in the sporo- 

 carp which, from the evidence of anatomy as well as of the ontogeny, is a 



