PARASITES. 



[ 492 ] 



PARMELIACE.E. 



tines, &c. of insects ; these appear to us to 

 be imperfect organisms (see Eccrtna, En- 



TEROBRYUS, ArTHROMITUS, LePTO" 



THRix, Cladophytum). — Several species 

 of Sphceria infest the larvae of insects, the 

 mycelium destroying them and gradually 

 completely displacing the internal organs, 

 while the skin retains its shape and dries ; 

 the fruit subsequently breaks out from the 

 anterior or posterior extremity (see Sphce- 

 ria). The species of Is aria, sometimes 

 described as parasites, appear to grow upon 

 dead insects. 



5. The microscopic parasites of Plants 



are very numerous, belonging all to the class 

 of Fungi. Much confusion exists in many 

 works between the true parasites and mere 

 epiphytes, and it is sometimes very difficult 

 to draw any line of demarcation. Among 

 the undoubted parasites are all the genera 

 and species of the family Uredinei, 

 together with a large portion of the other 

 genera of Coniomycetes, and the Ascomyce- 

 tous forms to which they mostly belong. 

 Among the Hyphomycetes may especially be 

 cited the genus Botrytis, B, infestans 

 being the potato-fungus. Fusisporium, 

 " OiDiuM," &c., form destructive mildews, 

 and among the Physomycetes, the Ery- 

 siPHES, and especially their mycelia (com- 

 monly forming spurious Oidia), are well- 

 known pests. Further particulars are given 

 under Potato-Fungus, Vine-Fungus 

 and Blight. 



BiBL. Ch. Rob. Hist. nat. des Vegetaux 

 Parasites, 2nd ed. Paris, 1853 ; Bseren- 

 sprung, Ann. Nat. Hist. xii. ; Siebold, Wag- 

 ner's Handwort. d. Phys. ; Hannover, Mid- 

 ler's Archiv, 1842, Bennett, Ed. Phil. Trans. 



XV. 



[We omitted Gamasus, Latr.,in its proper 

 place. It designates a genus of parasitic 

 Arachnida, of the order Acarina, and family 

 Gamasea. 



Char. Last joint of palpi smallest; labium 

 trifid ; mandibles cheliform, denticulate ; 

 body entire, with two dorsal plates; anterior 

 legs generally longest. 



The species are mostly parasitic upon 

 insects ; some are found running u})on the 

 ground ; others exist upon the higher 

 animals. 



A. coleoptratorum (PI. 2. fig. 26). Found 

 upon dung-beetles ( Geotrupes), &c. Anterior 

 coxae attached at a little distance from those 

 of the second pair ; tarsi (fig. 26 a) termi- 

 nated by two claws and an elegant pulvillus ; 



palpi of moderate length, with a moveable 

 seta like that of Dermanyssus; labium broad, 

 terminated by a median point and two lateral 

 hooks. 



G. marginatus. Found upon the human 

 brain ! also upon a fly. 



BiBL. Duges, Ann. d. Sc. nat. 2nd ser. 

 ii. p. 24 : Gervais, Walckenaer's Apteres, 

 iii. 215; Koch, Deutschl. Crustac. Mvriajj. 



PARASITIC FUNGI. See Parasites. 



PARENCHYMA. See Tissues, Vege- 

 table. 



PARKERIA, Hooker.— The typical genus 

 of Parkerieaeous Ferns. Aquatic ; exotic. 



PARKERIE.E.— A tribe of Exotic Poly- 

 podiaceous Ferns, consisting of aquatic 

 forms, in which the sporanges are not 

 gathered in sori, and with a habit very dif- 

 ferent from the majority of Ferns. 



Genera. 



I. Ceratopteris. Sporangia surrounded 

 by a broad, complete, articulated annulus, 

 placed u])on longitudinal veins. Spores 

 globose, trifariously streaked. 



II. Parkeria. Sporangia with an almost 

 obsolete basilar annulus, placed on longitu- 

 dinal veins. Spores three-sided, concen- 

 trically streaked. 



PARMELIA, Ach. — An extensive genus 

 of Parmeliaceae (Gymnocarpous Lichens), 

 characterized by their spreading, lobed, foli- 

 aceous thallus, with orbicular apothecia fixed 

 by a central point beneath, growing upon 

 trees, palings, rocks, stones, walls, &c. 

 About thirty British species exist ; P. parie- 

 tina, the yellow wall-lichen, is one of the 

 commonest plants of this family, and fur- 

 nislies a ready means of observing the struc- 

 ture both of the apothecia and the sperma- 

 gonia (PI. 29. figs. 1-3). 



BiBL. tlook. Brit. Fl. ii. pt. 1. p. 202; 

 Engl. Bot. pi. 194, &c. ; Schaerer, Enum. 

 Crit. Lich. Europ. Berne, 1850. p. 33 ; 

 Tulasne, Ann. des Sc. nat. 3 ser. xvii. pp. 

 66, 137. 



PARMELIACEiE.—A family of Gymno- 

 carpous or open-fruited Lichens, bearing 

 sessile shields, the borders of which are 

 formed by the surface of the thallus. 



Syiiopsis of British Genera. 



I. UsNEA. Thallus somewhat crusta- 

 ceous, rounded, branched, generally pendu- 

 lous, with a central thread. Apothecia cir- 

 cular, terminal or processes of the thallus, 

 peltate, nearly of the same colour, mostly 



