FILICINEjE. 
455 
out beyond it into a pencil of delicate filaments ; three (or three times three) large 
masses of it are attached at this point. The frothy mucilage with its cavities full 
of air thus forms a float for the macrospore, and bears on its surface the upper 
part of the ruptured sporangium. 
The sporocarps of the Marsiliaceae are much more complex and more firmly 
constructed than those of the preceding family. The sporocarp of Piliilaria is 
a shortly-stalked spheroidal capsule, standing apparently by the side of a leaf 
towards its ventral aspect. Its morphological significance is not yet fully under- 
stood. The capsule has a very thick hard 
wall, consisting of several layers of cells, 
and contains, besides a considerable quan- 
tity of soft succulent parenchyma, hollow 
chambers which extend from base to apex. 
Pilularia globulifera (Fig. 320) has four 
such chambers, P. minula two, and P. 
americana three. The external wall of 
each chamber bears a thickening along its 
median line of the inner surface throughout 
its whole length, and in this thickening 
runs a fibrovascular bundle. On this 
receptacle (placenta) the stalked sporangia 
are borne, forming a sorus which consists 
at its lower part mostly of macrosporangia, 
at its upper of micrOSpOrangia. Probably slobiUi/era below the middle, where the macrosporangia and 
microsporangia ma and mi are intermingled; g the fibro- 
each chamber has, at an early stage of vascular bundles, a hairs, ^ epidermis of the outer surface. 
development, an aperture at its apex, but 
it is not clear here, any more than in Marsilia, how far a comparison of the 
delicate tissue which invests the sorus to an indusium is justifiable, a comparison 
which is made by many botanists. 
The sporocarps of the various species of Marsilia are usually somewhat 
bean-shaped capsules with very hard walls, borne on long or short stalks, which 
arise either upon the ventral aspect of the petioles of ordinary foliage-leaves (Fig. 
317) or at their bases. Their stalks may be simple, bearing but one sporocarp, or 
forked, bearing many sporocarps. From a petiole several usually arise together. 
The stalk is continued along the posterior edge of the sporocarp (Fig. 325), giving 
off lateral branches right and left, which dichotomise and run towards the ventral 
edge. The ripe capsule is bilaterally symmetrical and contains two rows of chambers 
each of which extends from the ventral to the dorsal margin (Fig. 321, A, B). In 
the very young fruit, according to Russow, each chamber communicates with the 
exterior by means of a narrow canal opening on the ventral aspect. A thickening 
(placenta) runs along the external wall of each chamber, bearing the macrosporangia 
on its central ridge, and the microsporangia on its flanks ; thus each chamber 
contains a sorus consisting of two kinds of sporangia. When the sporocarp bursts 
it becomes evident (Fig. 325) that the soft internal tissue forms, as in Pilularia, 
a completely closed investment for each sorus. When mature the microsporangia 
contain numerous (4 x 16) spores, the macrosporangia but a single one. 
