BRITISH FERNS. 15 



is supposed to resemble a spread eagle, hence the specific name 

 of Aquilina given it by Linneus. The frond is killed by the 

 first frosts of autumn, however slight they may be ; it instantly 

 turns to a deep brown colour, but remains perfectly undecayed, 

 and frequently in an erect position during the whole winter. 



The form of the frond is nearly that of an equilateral triangle, 

 the base being somewhat but not materially the shortest of the 

 three sides. The naked portion of the rachis is rather more 

 than a third of the entire length of the frond ; it is green, and 

 rather pilose, rounded, and not " angular and sharp-edged, 

 wounding the hands severely," as stated in the " English Flora." 

 This statement must have crept in by some casual error, not 

 being at all applicable to the present species. The pinnae are 

 pinnate, and the pinnulae regularly cleft to their midrib, the 

 lobes being rounded and entire ; the first pinnula on the upper 

 side of each pinna being smaller, and often undivided. Under 

 ordinary circumstances all the fronds are fertile, but the apex of 

 each frond is commonly barren. 



In the fertile pinnulae the sides of the lobes 

 are reflexed, the extreme margin being bleached 

 and ragged, and forming a cover to the thecae, 

 which are arranged in a marginal series, and as 

 they approach maturity are gradually protruded 

 beyond this cover, and appear in two dark 

 lines, parallel to the midrib of the lobe, as 

 represented on the left side of the adjoining 

 figure. The transverse veins are placed alter- 

 nately on the midvein of the lobe ; they are forked almost 

 immediately on leaving the midvein, and the divisions are not 

 unfrequently again divided before reaching the margin ; all the 

 veins are continued to the extreme margin of the green or leafy 

 part of the lobe, and there enter a pulpy incrassated portion 

 of the indusium, in which they become divided and dis- 

 appear ; and from this incrassated part the thecae take their rise, 

 as far as I can discover, in a continuous line ; they are placed 

 between two covers, which I wdll call indusia, although it is 

 evident that both cannot be analogous to the indusium, in the 

 genera Polystichum, &c. These two indusia may be detached 

 with the thecae adhering to them : the exterior terminates in 

 a marginal fringe, or series of capillary segments. Owing to 

 the great and almost invincible elasticity of the refiexed portion 



