16 



Genus 3. LASTREA. 



GEN. CHAR. Sori nearly circular, seated upon the back of the 

 lateral veins ; covered by a rcniform iudusium attached by its 

 sinus. 



The ferns included in this and the following genus, Polystichum, 

 are by some botanists associated under the general name of Aspi- 

 dium, to which genus they are referred in " English Botany." A 

 difference in the form and attachment of the indusium has been 

 considered a feature of sufficient importance to warrant their divi- 

 sion. The name Nephrodium, originally suggested by Mr. Brown, 

 has given way to that of Lastrca, bestowed upon it by Presl in 

 honour of M. De Lastre of Chatelleraut. 



LASTREA THELYPTERIS. Marsh Fern. TAB. VII. 



Rhizoma creeping. Fronds lanceolate, pinnate : pinnse linear- 

 lanceolate, pinnatifid ; lobes oblong, obtuse, the fertile ones with 

 revolute margins. Sori submarginal. 



Lastrea Thelypteris, Presl. Aspiclium Thelypteris, Swartz. Smith. 

 Hooker. E.B. the fig. a mistake. Hemestheum Thelypteris, 

 Newman, Hist. Brit. Ferns, 123. Acrostichum & Polypo- 

 dium, Linn. 



A very local species, found only in a wet spongy soil, in marshes 

 and bogs; not unfrequent in England and Wales, but rare in 

 Scotland and Ireland. Where met with it is generally abundant, 

 in consequence of its creeping habit, which is not unlike that of 

 the common Brake (Pteris aquilina), the long, slender rhizoma 

 growing rapidly, and branching in every direction. It is a colonizer 

 of wet soils, as the latter fern is of dry ones. The fronds are of 

 two kinds, barren and fertile, and spring up at short intervals, 

 never in tufts: the barren ones make their appearance in the latter 

 end of April or the beginning of May, and in their ultimate growth 

 seldom attain more than a foot in height; the fertile, produced 

 about July, are taller, not unfrequently reaching three feet or even 

 four, tae lower half or two-thirds of the rachis being devoid of 

 pinnae. The lateral veins divide in pairs about halfway between 

 the mid-vein and the margin, anu, in the fertile fronds, bear the 

 sori, one on each division, forming thus an intromarginal series 

 just within the rccurvation. In maturity the sori become con- 

 fluent, and all traces of the reniform indusium are obliterated. 



The species is a very elegant one, and not at all difficult of cul- 

 tivation ; it docs not seem to be injured by moderate exposure to 

 the sun, provided the soil in which it is planted be sufficiently 



