68 HISTORY OF BRITISH PERNS. 



often spread and become confluent, so that almost the 

 entire under-surface of the frond is covered with the spore- 

 cases. The indusium is narrow, with its free margin entire ; 

 this soon becomes pushed away by the growing sori, and 

 is lost. 



This species is very variable. In dry and exposed places 

 it is small, and obtuse in its parts, whilst in sheltered, 

 shady places it is much drawn out or elongated. The ex- 

 treme states have been considered as varieties ; and it is 

 true that occasionally there occur plants of which this blunt- 

 ness seems characteristic, and to these the name of obtusum 

 is sometimes given ; while on the other hand, sometimes, 

 but rarely, the form in which all the parts are much nar- 

 rowed and very acute is met with, and this is called acutum. 

 These differences become less marked in the cultivated plants 

 than in those which occur in a wild state, and hence they 

 seem hardly to deserve to be considered as permanent 

 varieties. The species has also been met with having the 

 fronds variegated with white. 



The ordinary forms of the plant are very commonly met 

 with growing on rocks or old walls, and on hedge-banks in 

 a sandy soil. The latter situations, where they grow most 

 vigorously, are often beautifully adorned by the drooping 



