152 MOSSES WITH A HAND-LENS 



leaves are without midrib and are nearly always in two ranks and 

 usually flattened so as to lie in one plane, but in the great 

 majority of cases there is a third rudimentary row on the under 

 side which are called underleaves, or amphigastria by those de- 

 voted to technical names. The pedicel which corresponds to the 

 seta of the mosses does not, as a rule, grow much until the spores 

 are nearly ripe, when it elongates very rapidly. The pedicels 

 and capstiles are of a much more delicate structure than in the 

 mosses so that they disappear soon after the spores have escaped, 

 but the peculiar and characteristic scales or bracts around the 

 base of the pedicel often remain much longer and help greatly 

 in identifying species.- Immediately surrounding the base of the 

 pedicel is a tubular, somewhat three-sided organ called the inner 

 involucre or perianth, surrounding this is the outer involucre, 

 called simply involucre by many authors. This latter may be either 

 tubular or composed of separate leaf-like divisions of varied 

 shapes, called involucral leaves or bracts, or perichaetial leaves or 

 bracts, or simply bracts. Either one, or even both, of these 

 involucres may be lacking in some species. 



So far as possible gametophyte characters have been used in 

 the keys and descriptions and in the great majority of cases 

 identification is easy from this part of the plant alone. 



Owing to the difficulty of getting authentic material in condi- 

 tion suitable for use in making drawings, many drawings have 

 been borrowed from various sources to illustrate plants that 

 would otherwise have been illustrated with original work. 



KEY TO FAMIUES. 

 Plants leafy, mosslike in appearance except for the two-ranked leaves 



with midrib entirely lacking Scale Mosses (Jungermanniaceae). 



Plants consisting of a flattened green thallus, sometimes nearly 

 circular but usually elongated and branching. (See illustrations 



of Riccia, Marchantia, Anthoceros, etc.) A. 



A 

 I. Capsules, if present, immersed in the tissue of the plant. Plants 

 floating on the surface of still water or growing on the mud along 



the banks Riccias iRicciaceae in part) . 



Capsules raised well above the thallus. Plants often growing 



in mud but never floating 2. 



^. Stomata (in our genera) present, easily discernible with a lens 

 as small pores on the upper surface of the rather thick thallus; 

 capsule borne on a special stalked receptacle as in Mar- 

 chantia Iviverworts (Marchantiaceae). 



Stomata not present on the thinner thallus; capsules never 



borne on a special stalked receptacle 3. 



3. Capsules usually very long and slender, splitting into two valves 

 when ripe after the manner of a mustard pod, the slender hairlike 

 columella remaining in the center . Horned Liverworts (Anthocerotaceae). 

 Capsules globular or ovoid, splitting into four valves; columella 



lacking Thalloid Scale Mosses (Metzgeriaceae). 



