METZGERIACEAE 63 
Family ІП. METZGERIACEAE.* 
Apical cell of the gametophore never directly transformed into 
anarchegonium. Sporogonia arising from the dorsal surface of the 
gametophore or only apparently from an apex. This family con- 
tains all the Jungermanniales in which the gametophore is persist- 
ently thallose and also the forms transitional between the thallo- 
phytic and cormophytictypes. Тһе aberrant genera Haplomitrium 
and Calobryum do not occur, so far as is known, on the North 
American continent. The involucres of the sexual organs and of 
the sporogonium very rarely, if ever, represent true leaves. 
KEY TO THE GENERA OF METZGERIACEAE 
Seta very short, less than тапи, long; spores accompanied by sterile cells without 
Бөле thickenings. 
Ф gametophore suborbicular, the somewhat leaf-like peripheral lobes almost en- 
tirely concealed by the numerous subglobose, cylindrical-ovoid, or fusiform-clavate 
involucres ; annual. 11. Sphaerocarpus. 
Gametophore a somewhat elongated thickened axis, with conspicuous crowded ir- 
regularly succubous foliar expansions on either side ; perennial through the con- 
version of a large portion of the axis into a tuber. 
12. Geothallus. 
Seta 4-50 mm. long ; elaters always developed. 
Gametophore with quite clearly defined stem and leaves; root-hairs very long, 
6. Fo. 
mostly violet or vinous-purple. 16. Fossombronia. 
Gametophore thalloid, without ventral scales and without special gemmae-recep- 
tacles. 
Thallus rather fleshy, pinnately, palmately, or subdichotomously branched, the 
unistratose marginal lamina, if present, narrow and passing gradually into 
e costa; antheridia and archegonia on short lateral branches; spores 
unicellular. 13. Riccardia.t 
Thallus irregularly dichotomous, the wide unistratose margin passin ng gradu- 
ally into the jndistinct costa ; antheridia in loculi on the back of nd costa, 
archegonia in a cavity near its apex; spores guage at time of de- 
hiscence . Pellia. 
Thallus with a narrow costa sharply limited from е unistratose marginal 
um mostly dichotomous ; antheridia and archegonia on short ventral 
anches. Metzgeria (р. 75). 
ы thalloid, but the thin margin often with more ог less leaf-like lobes ; 
cavities near the bases of the lobes commonly occupied by Nostoc vA 
ventral surface bearing mee dentate scales; gemmae in long-nec пери 4 
iltaped receptacles arising from the dorsal surface near the ends of the lobes ; 
Spores unicellu Safin 
Underwood, Bot Gaz 19: 361. 1894. The < Jungermanniaceae anakrogynae " 
of he and of Schiffner аа 
T Sterile conditions of Riccardia pinguis and Pellia sp. may be easily conf 
See remarks under 2. pinguis 
