POLYPODIUM. 147 



very readily seen with a pocket-lens, a necessary aid, by 

 the bye, to the study of Ferns. 



The fronds grow from six inches to a foot in height, 

 nearly triangular, with the base shorter than the sides, the 

 stipes about equalling the leafy portion in length. They 

 are partially three-branched, but the lateral branches are 

 much smaller than the central one, and attached to the 

 stipes by a more slender rachis. The lower branches are 

 pinnate, with pinnatifid pinnse ; the upper branch pinnate, 

 with its lower pinnse again pinnate, and the upper ones pin- 

 natifid, as also is the apex of the frond and of the lower 

 branches. The pinnules or lobes have a distinct midvein, 

 with simple or slightly branched venules, near the termina- 

 tion of which, in a marginal series, the sori are produced. 



This is one of the few Eerns which are found in calca- 

 reous or chalky soils. It is rare, and local in its distribu- 

 tion, being, we believe, almost confined to rocky limestone 

 districts, and occurring chiefly in the northern and western 

 parts of the island. In cultivation it does not require so 

 much moisture and shade as most other Ferns, but a lime- 

 stone soil is not at all essential to its well-being. 



The names of Poly podium Robertianum and of Lastrea 

 Robertiana have been given to this species ; and the former 



