16 



A capsule contains 20 cells, sporules. A son consists of 40 

 capsules. Each pinnulro has 6 sori. There are 22 pinnulsB to each 

 pinnro. There are 40 pinna* 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 consiaer 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 Indusium. 



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. 



TJie following is a List of the Genera of the 'British Ferns. 



1. Sori nude. That is, not ( \' 

 covered by an Indusium. \ l 



2. Sori, covered by an Indu- 

 sium. 



4. Aspidium. 



5. Cystopteris. 



6. Asplenium. 



7. Scolopendrium. 



8. Pteris. 



9. Cryptogramma. 



10. Bleclmwm. 



11. Adiantuni. 



3. Thecae (Seed vessels) Open C 12. Trichomenes. 



cases at the edges of the \ 13. Hymenophyllum. 

 leaves. 



ThecsB, closed capsules, split- ( 14. BotrycJiium. 

 ting by a pore. < 15. Osmunda. 



Opliioylossum. 



( 14. 

 < 15. 

 ^16. 



Edwin Baily, Printer, Cirenccster. 



