STRUCTURE 
15 
under the surface of the ground. In other Ferns — the 
common Bracken is an instance — the rhizoma creeps quite 
underneath the surface, throwing up its fronds at intervals 
from its upper side, and sometimes descending to a consider- 
able depth in the earth, whilst the rootlets, which are thin 
and fibrous, insinuate themselves into the damp earth, or 
into the soft veins of rock or stone on which the Fern may 
be growing, drawing thence by absorption, and conveying to 
the stem and frond the essential moisture. When the 
rhizomas merely creep along the surface of the ground, they 
are frequently furnished with hairs, or thick scales, which 
give them a shaggy appearance, but serve as a protection 
to the succulent root- stock which they cover. These creep- 
ing stems are of various sizes in the various species, in some 
being little more than stout fibres, whilst in other species 
they are thick and fleshy. The rootlets, or root-fibres, are 
in the same way proportioned to the size of the rhizomas ; 
in the larger species growing to some thickness, and in the 
