STRUCTURE. 9 
unfolded the visible.” Each little part of these com- 
pound ferns is coiled in, the little branchlets in their 
coils, the main frond in its coil. Thus, at the end of 
April, the Osmunda regalis , Nephrodium cemulum , dila - 
tatum , and collinum will put forth tender balls and cro- 
siers ; a little later, and Aspidium angulare , Nephrodium 
spinulosum , Thelypteris , Cystopteris fragilis, and Aspic - 
nium Filix-foemina will appear ; later again, Aspidium 
aculeatum , Nephrodium uliginosum , rigidum , Oreopteris , 
Polypodium Robertianum and Phegopteris , and the £co- 
lopendrium will look forth; but June will have com- 
menced before Nephrodium cristatum , Polypodium vuU 
gare , and Pteris aquilina will have made their appear- 
ance. The main stem uncoils first, hence the crosier 
form ; then the branches or pinnse uncoil, and then the 
leaflets or pinnules ; the lobes unfold the last. In the 
fully developed frond each part is open to examination. 
First we have the stipes , or stem , except in the few in- 
stances where the frond is sessile or stemless, the leafy 
part springing at once from the caudex and the leaf-like 
portion of the frond : it is generally clothed at the base 
with chaffy scales, which are supposed to be torn frag- 
ments of the outer skin which invested the stem in its 
early infancy ; sometimes these scales are numerous and 
cover not only the stem but the rachis, sometimes they 
are few in number, found only near the base of the 
stem. That portion of the stem traversing the leafy 
part of the frond is technically called the rachis . The 
structure of a fern-stem is very curious : it has a kind of 
tissue peculiar to itself, called scalariform , because of its 
resemblance to a ladder. Different species have their 
tissue in different modifications of form. In the stem 
of Nephrodium Filix-mas there is an external circle of 
