Special Morphology and Classification. 327 
of generations Rhizocarpez do not differ from the other 
classes of Vascular Cryptogams. Salvinia (Fig. 447) is 
absolutely rootless. On the older parts of the plant the 
leaves stand in whorls of three, the two upper leaves of the 
whorl being aérial leaves with entire margins, the lower one 
a submerged leaf divided into very narrow root-like seg-, 
ments. 
The European genera of Rhizocarpeze are only three, which are 
classified, as follows, into two orders :— 
1. Marsileacee. Perennial plants creeping in mud; the micro- 
sporangia and macrosporangia are contained in the same sporocarp: 
Marsilea, Pililaria. | 
2. Salviniacee. Annual plants floating on water ; the microspo- 
rangia and macrosporangia are formed in different sporocarps : 
Salvinia. | 
Only one other genus is known in addition to the above, Azol/a, 
[belonging to the Salviniacex]. The sporocarps of several Australian 
species of Marsilea are known as ‘nardoo,’ and are used by the natives 
as an article of food. 
Crass XI. Lycopodtacee. 
The plants belonging to this class present so many 
diversities, especially in relation to their vegetative organs, 
that they might well be distributed into several classes. 
The true Lycopodiee (Fig. 450 A) have a procumbent stem 
which usually dichotomises repeatedly, the branches extend- 
ing in all directions. The Selaginellee (Fig. 450 B) have 
also a procumbent stem which branches dichotomously, 
but the branches develope only in one plane, so that the 
plant presents an external resemblance to the Junger- 
manniez among the Hepaticz. In both these families the 
leaves are simple, sessile, and with a single central vein ; 
but in the Lycopodiez all the leaves are of the same size 
and arranged spirally on the stem, while in the Selaginellez 
they are placed in four rows, and are of different sizes, the 
lateral rows consisting of larger, the upper and under 
