INTRODUCTION. 
11 
STRUCTURE. — The plants contained in this order long maintained a 
situation among the dorsal Ferns, though improperly, because their fruit is not 
dorsal but marginal, growing in a distinct and differently organized receptacle. 
The annulus corresponds in its functions, jointed appearance, and elasticity, to 
those of the last order, except that instead of its being a continuation of the 
stalk of the theca, it is placed obliquely or transversely (woodcut of Trichomanes, 
fig. e), and consequently the theca bursts vertically. For this reason, Ilymeno- 
phyllum and Trichomanes form an order separate from the Polypodiaceae. 
Besides the difference in the fruit, the texture of the leaves is much simpler than 
in the last order. The leaf-stalk of each native genus is quite smooth and round, 
and contains but one bundle of spiral vessels ; this is solid, and forms an axis. 
The thecae arise from the veins still more evidently than even in the preceding 
order, as the receptacle is in the place of a lobe of the leaf. The laminae of the 
lobe contracted form the valves of the receptacle, and its vein or nerve exists as a 
central column, upon which the thecae are seated ; in Hymenopliyllum the vein 
terminates within the receptacle (woodcut of Hynienophyllum, fig. c), in Tricho- 
manes it is prolonged much beyond (woodcut of Trichomanes, figs, a and b). The 
rootstock of Trichomanes is thick, black, and very hairy ; that of Hymenopliyllum 
very- long, creeping, and matted together. 
DISTRIBUTION. — “ Hymenophyllaceae, more impatient of drought than many 
of the Polypodiaceae, delight in shaded situations, where they are bedewed by 
frequent mists and the spray of waterfalls ; growing on damp rocks and stones, 
half binied amongst the Mosses that accompany them ; and like the Mosses 
rapidly shrinking or expanding with variations of moisture. Two of the three 
native species are rare in Britain, especially the Trichomanes, which is peculiar to 
Yorkshire, if it be not now extinct in England. Another, Hymenophyllum Tun- 
bridgense, is found in various counties of England and Scotland, varying from 
Devon and Sussex to the river Clyde in Scotland. The much more abundant 
H. Wilsoni, was so long confounded with the former species, that it has been 
supposed a rarer plant than it really is, for the greater number of localities 
assigned for H. Tunbridgense belong to FI. Wilsoni. This latter species ranges 
from Cornwall, northward, to Sutherland, and rises on the mountains of Wales 
nearly to 2000 feet, and not improbably more.” — Mr. Watson’s MS. 
OSMUNDACEiE. 
( Contains only the genus Osmunda.) 
Osmundack.e, Br., Kaulf., Lind., Hook., Agard. 
Osmundeje, Sprang. 
SCHISMATOPTERIDES, Willd. 
Spurias Gyrat.e, Swz. 
Rimat.-e, Mohr. 
Acrogyrat.e, Bernh. 
Exanxulat.-e of Modern Authors. 
STRUCTURE. — This order varies very little from the two former, except 
