MARCHANTTACEAE. 503 



red-piirple or brownish red, concolorous below, the dorsal surface vesieular- 

 areolate, soon becoming spongiose or lacunose-alveolate; main fc-egments 1-2.5 

 mm. wide; margins obtuse or subacute, naked; scales wanting or rudimentary; 

 transverse sections mostly 2-4 times as broad as high ; dorsal epidermis soon 

 indeterminate, the cells of the primary stratum subspheric, ellipsoidal or papilli- 

 form, irregularly collapsing or subpersistent, they or their successors finally 

 40-110/U. in maximum diameter; air-chambers elongate-polyhedral, separated 

 by unistratose lamellae; monoecious (rarely dioecious?); autheridial ostioles 

 elevated 75-250 m; spores at first yellowish brown, soon darkening and often 

 nearly opaque, 60-110 ^u in maximum diameter, distinctly angular, with a mar- 

 gin mostly 3-10 /i wide, the outer face marked with somewhat imperfectly 

 formed areolae usually 10-30 /a wide or those in the middle sometimes larger 

 (30-45 ju) and enclosing a free-ending spur or an isolated tubercle, the inner 

 faces with tubercles, short, free irregular ridges, or sometimes with imperfect 

 areolae, the older spores commonly tuberculate-papillate in profile. 



On wet grounds and in sink-holes, Great Bahama and Exuma Chain : — Vermont 

 to Alberta, Lower California and Trinidad ; Europe, Crystalline Riccia. 



2. Riccia violacea M. A. Howe, Ann. Mo. Bot. Gard. 2: 51. 1915. 



Thallus small, 1.5-4 mm. long, simple or 1-3 times dichotomous, irregularly 

 gregarious, rather obscurely and finely reticulate and dark green above, dark 

 violet or blackish at margins and on sides; main segments 0.6-1.15 mm. wide; 

 margins obtuse or rounded, commonly erect-connivent or inflexed on drying, 

 bearing especially toward the apex and often low on the sides numerous or 

 occasional violet or sometimes hyaline conic or subcylindric acute or obtuse 

 papillae 20-110 /* long and 25-45 /i broad at base; scales very short or rudi- 

 mentary, dark violet, rarely overlapping, commonly divided into a series of 

 small irregular often tooth-like laciniae^, each consisting of only a few cells ; 

 transverse sections 1.5-2 times as broad as high; dioecious (?); antheridial 

 ostioles elevated 20-150 /x^ often violet; spores soon fuscous and very opaque, 

 80-105^ in maximum diameter, obscurely angled or flattened-sphaeroid, desti- 

 tute of wing margins^ finely, irregularly, indistinctly, and almost uniformly 

 areolate over whole surface, the areolae 7-11 ^i wide, soon very obscure and the 

 spores appearing minutely and densely verruculose. 



On moist ground, Eleuthera : — Mona Island ; Porto Rico ; Cuba ; and northern 

 Mexico. Violet Riccia. 



Family 2. MARCHANTIACEAE Corda. 



Marchaxtia Family. 



Thallus (except in Dumortiera) with a distinct dorsal layer of air- 

 chambers, communicating -with the outside air by means of epidermal pores. 

 Ventral scales in two (or more) longitudinal rows. Antheridia and arcbe- 

 gonia borne on more or less definite receptacles; antheridial receptacles 

 discoid, sessile or stalked; carpocephala discoid, invariably stalked, the 

 stalk sometimes with one or two rhizoid-furrows. Sporopbyte differen- 

 tiated into a capsule, stalk and foot, the capsule forced through the calyptra 

 at maturity by the elongating stalk and dehiscing irregularly or by means 

 of a more or less distinct lid; elaters present in the capsule. Gemmae 

 discoid, present in two genera. About 25 genera and 200 species, widely 

 distributed, especially in warm regions. 



1. MARCHANTIA [Marchant f.] L. Sp. PI. 1137. 1753. 



Thallus branching dichotomously. Air-chambers with distinct boundaries, 

 forming a single layer; green cells in short, simple or branched filaments rising 



