May, 1906.] 
Key to Liverworts. 
539 
Indeterminately branching: leaves somewhat remote, round-obo- 
vate; perianth clavate— obconic. Antheridia axillarv on 
short lateral branches, arising near the terminal involucre. 
obconica Sttlliv. 
Riccia Micheli. 
1. Terrestrial forms growing in rosettes or irregular dichotomous 
forms. Fruit immersed in the upper side of the thallus, 
mostly protuberant above. Thallus with or without air- 
cavaties. 2. 
Aquatic plants floating in water or with its retreat rooting in mud 
and there fruiting. Fruit immersed in the lower side or the 
central groove of the thallus. Thallus with air-cavaties. 12. 
2. Thallus mostly without air-cavities. 3. 
Thallus with air-cavaties communicating with the upper surface. 1 1 
3. Thallus naked, without cilia and scales on the margin and under- 
neath. 4. 
Thallus with scales underneath, not ciliate or more or less ciliate 
at the margin and apices. 7. 
4. Spores small (60/i or less). 5. 
Spores larger (7.5-95/i), dark fuscous with deep reticulations 
(about 8 across the conve.x turface); divisions of thallus nar- 
row. arvensis Aust. 
.5. Thallus with wide divisions, thin and flat, with few rootlets; spores 
muriculate, spinulcse. tenuis Aust. 
Thallus with narrow divisions and numerous rootlets. 6. 
tt. Thallus thin, flbrous-reticulate; spores obscurely muriculate. 
Frostii Aust. 
Thallus canaliculate above, carinate-thick-ened beneath; spores 
coarsely reticulate. 
{fluitans, L. var. Sullivanti, Aust.) Huebeneriana Lindenb. 
7. Thallus with scales underneath, not ciliate. S. 
Thallus more or less ciliate at the margin and apices. 10. 
5. Scales and usually the thallus purple underneath; scales not ex- 
ceeding the margin; spores light brown. nigrella D. C. 
Scales usually whitish; thallus green underneath. 9. 
9. Scales reaching beyond the margin: spores light brown. 
lamellosa Raddi. 
Scales not reaching the margin; spores dark brown. 
{sorocarpa Bischoft) minima L. 
10. - Capsules usually in a single row; spores blackish, opaque, scarcely 
reticulated {arvensis Aust. var. hirta Aust.) hirta Aust. 
Capsules scattered chiefly near the base of the divisions (with a 
purple spot near them on the thallus) ; spores brown, reticu- 
lated with 7-8 areolae across the convex surface. 
Lesciiriana Aust. 
11. Upper surface of thallus strongly pitted, green or reddish to pur- 
plish; divisions of thallus rather broad, obtuse or often obcor- 
date at the apex. crystallina L. 
Upper surface of thallus mostly smooth (except for the median 
groove), yellowish green; divisions narrow, linear, obcordate 
and convex, thickened at the apex. lutescens Schwein. 
12. Thallus linear, dichotomous, floating or rarely terrestrial capsule 
protuberant from the lower surface. fluitans L. 
Thallus obcordate, floating or rarely terrestrial; capsule not pro- 
truding, at last exposed by a cleft in the central groove. 
natans L. 
Scapania Dumort. 
1. Lower leaf lobe equalling in size the upper or nearly so. 2. 
Lower leaf lobe (except those near the summit) about twice the 
size of the upper or 3-4 times its size. 3. 
