GENERA AND SPECIES. I2I 
PLATE XLVII. 
TRICHOMANES. Linnzus. 
Gen. CHAR.—Fruit-dots marginal, at the ends of free veins; in- 
dusium urn-shaped, cylindrical, in which the sporangia are borne 
upon an elongated receptacle (columella); the frond delicate and 
pellucid. 
The genus Trichomanes is the only representative of the 
sub-order Hymenophyllacee in this country. It differs 
widely from any of the ferns yet described, not only in 
the form and arrangement of the sporangia, but in the 
peculiar texture of the foliage, and the disposition of the 
capsules upon the frond. The pellucid appearance of the 
leaf-tissue is common to all the Hymenophyllacez. This 
transparency is due to the fact that the fronds have but a 
single layer of cellular tissue, while the darker veins are 
composed of several layers of compact tissue. In many 
respects they resemble mosses more than true ferns; and, 
accordingly Prof. Sachs assigns them the lowest place in 
the fern family, next to the mosses. But the unfolding of 
the leaf, as well as the venation, is exactly like that of the 
true ferns. 
The sessile sporangia are situated upon a long columella, 
inclosed in an urn-shaped involucre, upon the ends of the 
free veins at the margin of the leaf. The apex of the urn- 
shaped body does not project beyond the margin of the 
lobe of the pinnule, but the column or bristle is prolonged 
beyond it a quarter of an inch. This column, under the 
microscope, presents a series of spiral scars at the points 
where the sessile sporangia have been attached. 
The ferns of this group are confined to damp, secluded 
situations, shrivelling up when exposed to the direct rays 
II 
