50 FERN'S. 



ranged in the form of transverse bars, somewhat 

 resembling the steps of a ladder ; which structure is 

 best seen in a transverse or slightly oblique section. 

 The fronds are usually cleft nearly down to the main 

 vein or midrib (fig. 9), or pinnatifid (pinna, a feather, 

 findo, to cleave); sometimes the segments are simi- 

 larly cleft, so that the fronds are bipinnatifid. The 

 manner in which the veins usually branch is also 

 peculiar, each branch separating from the point of 

 division at an acute angle with the original direction 

 of the vein (fig. 20), so as to be forked. It is also 

 worthy of notice, that the young frond is rolled up 

 into a flat spiral, or is cir'cinate (circino, to go round), 

 before it opens. 



We will now examine one or two species more 

 minutely. 



POLYPODIACE./E. Polypodium vulgdre (PL II. fig. 9, 

 one-third of the natural size), a member of this 

 family, is very common on old trunks of trees, on 

 banks, &c. The frond is deeply pinnatifid, the seg- 

 ments being oblong, blunt (obtuse), scalloped (cre- 

 nate) at the edges (PL II. fig. 10), and becoming 

 gradually shorter towards the apex of the frond. 



On the back of the fronds are the little orange- 

 coloured groups of capsules (PL II. figs. 9 & 10); 

 these are called sor'i (atopos, a heap) . The capsules 

 or thecce (Otf/cr), a case), a magnified group of which is 

 represented in fig. 11, consist each of an aggregation 

 of cells, fixed to a stalk (fig. 12) ; and along the back 

 of the capsule is a close row of thicker cells, forming 

 an elastic ring, the annulus. When the seed-like 

 bodies or spores (o-Tropa, a seed) are ripe, the annulus 

 becomes straightened from its elastic power, and tears 

 the capsule open, so that the spores are set free and 

 scattered. 



Aspid'ium filix mas (PL II. fig. 16, reduced to one 

 third.or fourth of the natural size), is the most common 

 British fern. In this the fronds are pinnate, i. e. the 



