THE STRUCTURE OF FERNS. 19 



tongue, in both of which the fronds in tlie undeveloped 

 state are folded straight. 



The substance of the fronds is traversed by veins va- 

 riously arranged ; in some species forming straight, nearly 

 parallel lines, in others joined together like network. The 

 manner in which the veins are disposed is called the 'cena- 

 tlon, and the nature of this venation affords useful data in 

 the division of the ferns into family groups. It is from 

 some determinate part of these veins that the clusters of 

 fructification proceed, that part to which they are attached 

 being called the receptacle. 



A correct appreciation of the condition and position of 

 the receptacle with reference to the veins, is of considerable 

 importance in the study of the genera and species — that is 

 to say, the family groups and the individual kinds. In 

 some, tliough few, of the native kinds, it is projected be- 

 yond the margin, and the little cases of seeds are collected 

 around its free extremity. More commonly, however, the 

 veins stop within the margins, and the seed-cases groAV in 

 round or elongated clusters, situate in some cases at their 

 ends, in others along their sides, and protruded through 

 the skin of the lower surface of the fronds. 



No flowers are produced, but the plants bear, generally, 



c 2 



