DEFINITIONS OF TERMS. 1$ 



margin. Where there are no indusia the sori are said 

 to be non-indusiate, or naked. In some species the 

 margins of the pinnules are turned back 

 over the sori and cover them after the 

 manner of indusia. The fructification, in 

 such cases, is produced close to the ex- 

 treme outer edges of the leafy parts of the 

 frond, and is then said to be marginal. 

 In the case of those sori covered by 

 indusia when the spores are ripened, the indusia dry 

 up and fall off, and the spore-cases enclosed themselves 

 burst and liberate the infinitesimal germs they contain. 

 We shall see presently what is the shape of some spores 

 and spore- cases. 



Fructification is a term applied to the general system 

 of spores. Some fronds bear no fructification, in which 

 case they are said to be barren; whilst others, upon the 

 same plant, are spore-bearing, and these are called! 

 fertile fronds. The fructification, as we have seen by 

 the magnified figures on page 14, is attached to the 

 veins which ramify over the leafy substance of the 

 frond. The system of veins is called the venation. That 

 particular portion of the venation to which the fructifica- 

 tion is attached bears the name of the receptacle. 



Into a detailed consideration of the question of classi- 

 fication it is not the design of this volume to enter. 



Ferns constitute a great class of the vegetable king- 

 dom. According to one of our botanical systems this 

 class is subdivided into orders, the orders into genera, the 

 genera into species, the species into varieties. In the 

 botanical arrangement of British plants under this par- 

 ticular system ferns belong to the third class called 

 Acotyledons or Cryptogams (the other two classes of plants 

 being, i, Dicotyledons ; and, 2, Monocotyledons}. These 

 collective expressions are used to indicate that the 

 plants which are designated by them are produced from 

 seeds which are of three kinds: i, seeds which have 



