PILULARIA.—SALVINIA. O71 
‘this cavity is gradually filled up with cellular tissue, constituting 
a conical prothallium confluent with the nucleus. A single 
archegonium is formed in the centre, the orifice of which corre- 
sponds with the apex of the prothallium.’ Fertilisation takes 
place by means of the antherozoids of the microspores. 
The aitheridia or male organs contain a number of small 
cells (fig. 818), which ultimately develop long spiral anthero- 
zoids. These small cells are called pollen spores, small spores, or 
microspores. ; 
In Pilularia the fructification consists of stalked, pill-shaped, 
hairy sporocarps. The interior of each sporocarp is divided 
usually into four cells (fig. 819), and when ripe it opens by four 
valves. In the interior of each cell there is a mucilaginous pro- 
cess or placenta attached to the walls, upon which are placed 
numerous antheridia and sporangia, as in Marsilea. The struc- 
ture of these antheridia and sporangia resembles in all essential’ 
Fic. 818. Fie. 820. 
Fie. 819. 
Fig. 818. Antheridium of a species of Marsilea containing microspores. After 
Le Maout. Fig. 819. Transverse section of the sporocarp or spore fruit 
of Pilularia globulifera. After Henfrey.— Fig. 820. Vertical section of 
the sporocarp of Salvinia, showing sporangia in one cavity, t, and anthe- 
ridia in the other cavity, a. 
particulars those of Marsilea. In fact, the only difference 
between the fructification of Marsilea and Pilularia is the more 
complicated nature of the sporocarps in Marsilea. 
The fructification of Salviinia (fig. 820) appears to resemble 
that of Marsilea and Pilularia, except that the antheridia, a, 
and sporangia, b, are here contained in separate sacs, and are 
attached to a sort of central cellular placenta. In germination, 
also, the prothallium of Salvinia differs from that of Marsilea 
and of Lilularia, in producing several archegonia, instead of 
only one, as is the case with them. From these causes the 
Marsileaceze are frequently divided into two orders, namely, 
Marsileacez and Salviniaceze, the former including the genera 
Pilularia and Marsilea, and the latter those of Salvinia and 
Azolla. The common name of Rhizocarpez is also frequently 
applied to the two combined orders. 
BB2 
