GENERA AND SPECIES. E17 
PLATE XLV. 
DICKSONIA. L’Heritier. 
GEN. CHAR.—Fruit-dots very small, marginal, at the apex of a 
free vein or fork; indusium cup-shaped, membranaceous, opening at 
the top, and partly adherent to the reflexed margin. 
This genus, named in honor of James Dickson, a noted 
English cryptogamic botanist, furnishes some of the most 
noble and graceful specimens of the vegetable kingdom— 
the Tree Ferns of the tropical islands of the Pacific and 
Indian oceans. The form and arrangement of the organs 
of fructification, however, as in other ferns, determine their 
place in the order of Filices. A single unpretentious spe- 
cies represents the genus in this country. ’ 
It belongs to the tribe Davalliez, characterized by its 
having the sporangia inclosed within a slightly-recurved 
lobe of the pinnule. A magnified view of the pinnule, 
showing the venation and the position of the fruit-dots, is 
given in the Plate. Figure 2, still more magnified, shows the 
reticulated structure of the leaf-tissue and the cup-shaped in- 
dusium or involucre bursting and discharging the sporangia. 
Hooker, in his “ Genera of Ferns,” says that “the indu- 
slum or involucre appears to be formed of a dilated (at 
length membranaceous) portion or tooth of the frond, 
which unites with a scale arising from the apex of a nerve 
on the under side of a pinnule.” There is formed, at 
first, a nearly globose, entire indusium, which soon bursts 
at the top, sometimes with a transverse cleft, and some- 
times with an irregular circular opening. In all the speci- 
mens which I have examined the opening was irregular. 
A number of delicate microscopic hairs may be found 
on the margin of the indusium. 
