72 HOW TO KNOW THE FERNS 



dark green colour, and these are of a somewhat 

 leathery nature. In a fair-sized example the 

 frond is twice pinnate, the pinnae are definitely 

 stalked, and the pinnules are roughly wedge- 

 shaped, being somewhat toothed at the lip. 

 The Wall Rue is excessively variable, and in 

 exposed places it is possible to find plants 



Back of frond of Asplenium ruta-muraria. Enlarged. 



bearing fronds which are only divided once, 

 the pinnae being segmented. 



The son are in the form of lines which branch 

 out from the lower part of the pinnule in a 

 fan-shaped manner. The indusium disappears 

 as soon as the sporangia become mature, and 

 eventually the son may spread over the whole 

 of the back of the pinna or pinnule. 



