



114 THE BRITISH FERNS. 
redistribution of the species. Professor Fée, indeed retains the name 
of Aspidium for the Lastrea group, on the ground of its containing 
the larger proportion of the original species; but it seems more 
consistent to retain the typical plants of Swartz, and no species 
has so strong a claim to be considered typal as A. trifoliatum, to 
which the name was allotted by Schott. Swartz assigns the cha- 
racters ‘Sori subrotundi, sparsi; indusio umbilicato 1. dimidiato 
tecti" to his genus Aspidium, thus giving precedence to the umbi- 
licate, d. e. peltate indusium. Hence, therefore, A. trifoliatum, 
the first peltate species in his enumeration, may fairly be considered 
typal, and this has reticulated venation. 
The peculiar characteristics of the genus Polystichwm consist in 
the punctiform sori being dorsal on the free veins, and covered 
by circular peltate indusia. It consequently differs from true 
Aspidium as above indicated, in the free instead of reticulated 
venation; whilst from Lastrea, with which it agrees in having 
free veins, it differs in having peltate instead of reniform or 
dimidiate indusia. From Polypodium, the Phegopteris section of 
which has similarly placed punctiform sori, it is distinguished by 
the presence of the indusium. 
Polystichum is not always readily known from Polypodium, on 
account of the fugacious character of the indusium in some species, 
for if this is cast off in an early stage, as it frequently is, nothing 
remains by which to distinguish them. There are some exotic 
species, not very satisfactorily determined from this cause: being 
only known from herbarium specimens in which it is uncertain 
whether the indusium has never been present, or has been cast off 
while young, the sori being apparently naked from whichever cause. 
Polystichum is an extensive genus, consisting for the most part 
_of harsh evergreen spiny-toothed Ferns, scattered from the torrid 
to the frigid zones, and represented by two or three species in 
our own country. These species are so variable, and so thoroughly 
connected by intermediate forms, that it is difficult to come to 
a conclusion as to their limits which is perfectly satisfactory to 
botanists generally. Some persons admit three native species, 
and we adopt this view; others refer all the forms to two species. 
The series is so perfect from beginning to end, that it appears to 

