POLYPODIUM. 
79 
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 pinnae ; 
the upper branch pinnate, with its lower pinnae again 
pinnate, and the upper ones pinnatifid, 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 termination of which, in a mar- 
ginal series, the sori are produced. 
This is one of the few Ferns 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 this species does not 
require so much moisture and shade as most other Ferns, 
but a limestone soil is not at all essential to its well-being. 
The names of Polypodium calcareum^ Phegopteris cal- 
carea^ Lastrea Rohertiana^ and Gymnocarpium Robertia- 
num, have been given to this species. 
