THE BLADDER FERNS. 
359 
higher ones. These lowest branches are again 
divided, each having above and below its mid-stem 
a row of leaflets. But the upper row of leaflets, 
near the main rachis, are much shorter than the 
lower row, and are deeply cleft or serrated. The 
two leaflets of the lower rows nearest the main 
rachis are so much developed, that at and near 
their base they are again divided into lobes, which 
in their turn are serrated. Curiously enough, 
however, the disproportion between the size of the 
leaflets on the upper and lower sides diminishes 
towards the point of the branch, and the process 
of division into lobes is also reduced gradually, so 
that near the tips of the branch the opposite leaflets 
are equal in size, and being then much smaller 
than those at the base of the branch, are not again 
divided into lobes, but are simply jagged or 
serrated at their edges. Leaving now the lowest 
pair of branches on the frond, and coming to those 
immediately above them, we find that this pair, 
besides being much smaller, has not the same 
disproportion between the upper and lower leaflets, 
although those of the upper row are somewhat 
shorter than those of the lower one. On this 
