PREFACE. 
XVII 
rule, the sori are developed upon the under side of the 
fronds, the spiked and panicled fruit of Acrostichum, 
Aneimia, &c., Osmunda, Botrychium, and Ophioglossum, 
being the exceptions. But, among our native Ferns, the 
sori are sometimes observed upon both sides of the fronds, 
as in Asplenium Trichomanes, and Scolopendrium vulgare, 
N.F., plate 52a, f. 619, 760: the common Polypody also 
rarely showing the same character, N.F., £ 35. 
In the Moonwort, the lamina frequently exhibits sori 
upon its cut edges (Plate 23) ; and, vice versa, the summit 
of the soriferous frond becomes leafy: this last change is 
occasionally met with in Osmunda regaiis, assimilating the 
species to the Canadian 0. Claytoniana. Linn. 
The conversion of the Sori, or rather of the capsules of 
fruit, into bulbils is a conspicuous feature in exotic, and 
occasionally in native Ferns. In Asplenium Belangerii and 
Viviparum, the young plants, thus produced, differ greatly 
in their primary fronds from the parent plant, f. 12. The 
sori of a frond of Pteris quad- 
riaurita, gathered in Ceylon, 
vegetated copious rootlike pro- 
cesses. The fruit spikes of 
Selaginella cuspidata Link (f. 
13), frequently yield perfect 
plants (f. 13a), especially at the 
extremity of the older fronds, 
this most interesting species, which abounds 
upon the high table-lands above Tepic in Mexico, 
rolls up in the dry season into a nestlike ball, 
including the young plants upon its fronds, be- 
comes detached from the soil, and is driven 
about, loose, by the wind ! Upon the return of 
the rainy season, however, the plant expands, 
the outer and often leafless fronds curving back 
and fixing themselves firmly in the soil, while 
the development of new roots cfives a central 
Fig. 12 . 
