XVII. OSMCNDA. 213 
upwards, acquiring a resemblance to the trunks of the tree 
ferns is very firm, and beset with numerous strong fibre;*. 
The fronds are circinate in vernation, and when quite 
young are very tender, shooting up with rapidity, and 
attaining sometimes the height of ten or twelve feet in 
damp sheltered spots, and from two to four feet in more 
exposed and drier situations ; they are developed in May. 
and destroyed by the early frosts. The stipes is stout, 
smooth, without scales, variable in length, and as well as 
the rachis succulent and tinged with red while young, 
but becoming woody. Some fronds are entirely barren, 
others bear fructification, the latter differing from the 
former only in the presence of the panicle of spore-cases. 
The fronds are lanceolate, bipinnate, with the nearly 
opposite pinna; arranged in pairs ; they are erect, or less 
frequently and chiefly when growing by water, somewhat 
pendulous. The pinnse are lanceolate or ovate-lanceolate, 
with opposite or alternate pinnules ; the latter of an oblong 
r oblong-ovate form, blunt at the apex, somewhat dilated 
and auricled at .the base, especially on the posterior side, 
and often serrated ; the apical pinnule being usually some- 
what more acute than the rest. The venation is very dis- 
tinct : each pinnule has a prominent midvein, the veins 
from which are forked almost at their base, the venules 
being usually again divided, running in parallel lines, and 
terminating in the margin. The fructification consists of 
the upper pinnae changed from the leafy to a soriferous 
state, and forming a more or less compact panicle of 
spikes, covered over with spore-cases, attached to the veins 
of the altered pinnules, of which only a slight wing is de- 
veloped on each side the midvein. Not unfrequently 
the pinnules on some of the pinnae are but partially trans- 
formed, a few masses of sori occurring at the base, while 
the apex remains leafy. Sometimes the pinnse near the 
apex become soriferous, while the extreme apex itself re- 
mains leafy and barren. These modifications indicate the 
true nature and origin of the fructification. The spore- 
