CETERACH. 
153 
developed fronds, prettily contrast with the deep green of 
the upper surface. , The pinnae or lobes are of an ovate 
form, and either entire or lobed on the margin. 
The opacity of the fronds renders the venation indis- 
tinct, and indeed it is only to be made out by examining 
young fronds, removing the covering of scales, and the 
outer skin of the frond itself. It is then seen, that from 
the lower corner the principal vein enters, taking a sinuous 
course towards the upper side of the apex ; it branches 
alternately, the veins being again branched, and the 
venules becoming joined more or less near the margin. 
The sori are borne along the sides of the venules in a very 
irregular manner, the majority of them being directed 
towards the apex of the pinna. At first, the sori are 
quite concealed by the scales, but the spore-cases ulti- 
mately protrude between them, although, being very similar 
in colour, the latter are never very obvious. 
The Ceterach is a mural species, occurring on the walls 
of old buildings and ruins, and in rocky places. It is 
pretty generally distributed in the United Kingdom, but 
is considered somewhat rare in Scotland. It occurs also 
throughout central and southern Europe, and in the north 
of Africa. In the Canaries^ a closely-allied but much 
