16 
A capsule contains 20 cells, sporules. A sori consists of 40 
capsules. Each pinnule has 6 sori. There are 22 pinnule to each 
pinne. There are 40 pinne to each frond. There are 8 fronds 
to each root. 
Hence 20 X 40 x 6 X 22 X 40 X 8 = 33,792,000. 
The necessity for the production of so many seeds is explained 
when we consider that ferns cannot grow everywhere; hence the 
casualties to which they are liable are amply provided for. 
The clusters of capsules, in most instances, begin forming be- 
neath the epidermis, and attach to the nervures on the under side 
of the frond, the epidermis remaining as a protective covering 
until the seeds are ripe, when it dries up. The form and disposi- 
tion of this membrane, which is analogous to the Calyx, differs in 
different genera and species; it is called an Involucre or Indusiwm. 
In as far as British Ferns are concerned, we may divide them 
into genera, depending upon the presence or absence, the disposi- 
tion, and form of the parts heretofore described. The species 
being dependent, for the most part, upon the form of the divisions 
of the frond. 
The following is a List of the Genera of the British Ferns. 
1. Ceterach. 
2. Polypodium. 
. Woodsia. 
1. Sori nude. That is, not 
covered by an Indusium. 
3 
4, Aspidium. 
5. Cystopteris. 
6. Aspleniwm. 
7. Scolopendrium. 
8. Péeris. 
9. Cryptogramma. 
10. Blechnum. 
. Adiantum. 
i 
. Trichomenes. 
1 
3. Thecze (Seed vessels) Open (1 
18. Hymenophyllum. 
1 
1 
ci 
cases at the edges of the 
leaves. 
Thecx, closed capsules, split- 
ting by a pore. 
. Osmunda. 
. Ophioglossum. 
2. Sori, covered by an Indu- 
sium. 
1 
2 
3 
4. Botrychiwm. 
5 
6 
Edwin Baily, Printer, Cirencester. 
