362 HYMENOPHYLLUM. PART 11. 



elongated cup around the prolonged vein. At the 

 base of that vein the sporangia form a small globular 

 cluster ; and, as they advance towards maturity, the vein 

 extends in the form of a bristle, far beyond the mouth 

 of the cup (fig. 68). The cup is winged in the more 

 luxuriant form of the plant, in consequence of the double 

 layer of tissue composing the segment to which it be- 

 longs not separating through its whole breadth. The 

 cup-like cylinder being slightly compressed in the plane 

 of the frond is indicative of its origin. 



A slight difference in fructification separates the Hy- 

 men ophyllum tunbridgense, or Film fern (fig. 69), from 

 the Trichomanes, for both have 

 a creeping rhizome, from which 

 single fronds spring at short in- 

 tervals. The leafy parts of the 

 fronds are merely winged veins, and 

 the wings consist of two layers of 

 cellular tissue finely reticulated. 

 The Hymenophyllum is distin- 

 guished from the Trichomanes by 

 a two-valved cup spinously ser- 

 Fig ' 6 tu n bri% e ense hyllum rat ed, which completely conceals 

 the fruit-bearing vein, while, in 



the Trichomanes, the cup is more cylindrical, smooth- 

 edged, with the fertile vein projecting far beyond it 

 (fig. 68). The beautiful little Film fern, with its semi- 

 transparent fronds not more than two or three inches 

 high, grows on shady wet rocks, among the moss on the 

 branches and roots of old trees, and on the ground 

 near lakes and rivulets. It is hardy enough to live in 

 the Highlands of Scotland ; but the H. unilaterale, a far 

 less beautiful plant, has its limit in Unst, the most 

 northern of the Shetland Islands. The fructification in 

 the latter plant, though the same in position, is stalked 

 instead of being sessile. The involucre is rounded and 



