STRUCTURE 
21 
other, as they are alternately unrolled, the same process. 
In the same way also, so soon as the pinna), beginning with 
the lowest, which are always, as we have seen, the first to be 
liberated, are left free from the principal coil of the frond, 
they, if compound — i.e. containing pinnules and lobes — set in 
motion the same process, the first unrolling taking place — 
the rolling being always from base to apex either of pinnule 
or lobe — at that part of the pinna next the principal rachis. 
The unrolling by alternation goes on in the same manner 
throughout the whole length of the frond, the highest pinna) 
being the last to be unrolled. Briefly, then, the process 
may, as we have seen, be described to be — in fronds other 
than those which are simple — the unrolling of the principal 
coil from base to apex, followed in alternation by the lateral 
and perpendicular unrolling of pinna), pinnule, and lobe. 
The chaffy and various-coloured — though usually brown 
or rust-coloured — scales, which, as we have noticed, are 
frequently found clothing the stipides of Ferns, are, in a 
number of the species, continued along the backs of the 
rachis and its branches sometimes covering the entire under- 
surface of the fronds, and giving to them, in such cases, a 
remarkably hairy or shaggy appearance. In some of the 
species the scales give a singularly beautiful appearance to 
the fronds. As to the size and arrangements of these scales, 
they are found to be largest at the base of the stipes, getting 
smaller upwards, and being smallest at the highest point of 
the primary rachis, and at the points furthest from the bases 
of its branches. 
We have now to indicate the characters which especially 
serve to distinguish Ferns from other plants. Under what 
is called the ‘ natural system ’ of botany the vegetable king- 
dom is divided into two great groups of plants, namely, 
flowering and flowerless plants. At the head of this latter 
division stand the Ferns. These beautiful plants, however, 
