RHYTISMA. 



[ 553 J 



RICCIE.E. 



RHYTISMA, Fries. A genus of Phaci- 

 diacei (Ascomycetous Fungi), growing upon 

 the leaves of trees and shrubs, forming dark 

 patches or spots on the surface, breaking 

 through the epidermis in little scales or 

 irregular fissures. -R. acerinum is exceed- 

 ingly common, forming large black spots on 

 the leaves of the sycamore and maple ; the 

 thecasporous fruit is perfected (on the dead 

 fallen leaves) in spring ; MELASMIA aceri- 

 na, which occurs in autumn, appears to 

 be a preparatory form of this plant. R. 

 salicinum is common on willow-leaves. 



BIBL. Berk. Brit. Flor. ii. pt. 2. p. 290 ; 

 Grev. Sc. Crypt. Fl. pi. 118; Fries, Summa 

 Veg. 3/0; Tulasne, Comptes Rendus, March 

 31 st, 1852 (Ann. Nat. Hist. ser. 2. viii. 

 p. 118). 



RICCIA, L. A genus of Riccieae (Hepa- 

 ticacere), consisting of minute green thalloid 



Fig. 625. 



Riccia fluitans. 



Lower surface of a fragment of the frond, with three 

 imbedded sporanges projecting, their orifices being on 

 the upper surface. 



Magnified 5 diameters. 



productions growing upon damp ground or 

 floating on water, distinguished from the 



Fig. 626. 



Fig. 627. 



Riccia fluitans. 



Fig. 626. Vertical section through the frond or sporange 

 contained in its substance. 



Fig. 627. Sporange with persistent epigone, extracted 

 from the frond. 



Magnified 25 diameters. 



allied forms by the capsules being immersed 

 in the substance of the frond, destitute of 

 perichsete and perigone, while the archegone 



pt naiiently encloses the sporange as an 

 adherent epigone, bearing a persistent style- 

 like neck (figs. 626, 627). The antheridia 

 are globose sacs contained in special cavities, 

 the orifices of which, narrowed into a neck, 

 project as short processes from the surface 

 (cuspides). The epigone being adherent to 

 the sporange, the spores appear to lie im- 

 mediately in the cavity of the former when 

 ripe ; they are unaccompanied by elaters and 

 escape by irregular rupture of the epigone. 

 Several species occur in Britain. 



* Terrestrial. 



1. R. glauca, L. Frond without mem- 

 branous scales below, fleshy, ovate-oblong, 

 two- to three-lobed, 1-2 to 1" in diameter, 

 the divisions dichotomous, growing in orbi- 

 cular tufts, surface smoothish, punctate, 

 glaucous green. On banks. 



2. R. crystallina, L. Differing from the 

 last chiefly in larger size and lighter colour, 

 and having large cavernous air-cells opening 

 widely on the upper surface. Damp mould. 



** Aquatic. 



3. R. fluitans^. (fig. 625). Fronds with- 

 out scales below, 1-2 to 2" long, repeatedly 

 forked, segments linear, notched at the 

 ends; when placed on damp earth it produces 

 radical hairs (fig. 626-7). Stagnant water. 



4. R. natans, L. Fronds with long reti- 

 culated scales below, obcordate, 1-2" long, 

 or with the two lobes again divided; scales 

 of the lower surface purple. On stagnant 



BIBL. Hook. Brit. Flora, ii. pt. 1. p. 102; 

 Bischoff, Nova Acta, xvii. p. 909 ; Linden- 

 berg, ibid, xviii. p. 361 ; Hofmeister, Ver- 

 gleich. Untersuch. p. 43. pi. 10. 



RICCIEAE. A tribe of Liverworts or He- 

 paticacea3, consisting of delicate green mem- 

 branous fronds, spreading on the ground or 

 floating on water. The fruits are always 

 sessile on the frond, more or less imbedded 

 in its substance, according to the thickness ; 

 the spores are unaccompanied by elaters. 



Synopsis of British Genera. 



I. SPH.EROCARPUS. Archegones dorsal, 

 on a lobed membranous frond, sparingly 

 aggregated. Perichsete obtusely conical or 

 pear-shaped ; perforated at the summit, con- 

 tinuous with the frond. Perigone wanting. 

 Epigone crowned by the deciduous style. 

 Sporange at length free, indehiscent. 



