i6o 



MOSSES WITH A HAND-LENS 



place from which the female receptacle will develop, but the scales 

 are much fewer in number and are like hairs, while in Grimaldia 

 they are ^ of an inch or more wide. 



METZGERIACEAE. The Thalloid Scale Mosses* 



The spore bearing portion of plants of this family is like 

 that of the Scale Mosses, but the green part of the plant is a 

 thallus instead of a leafy stem in nearly all cases. There are, 

 however, some intermediate forms in the family in which the 

 thallns is divided into leaflike lobes. The thallus is much less 

 highly differentiated than in the Liverworts and Ricchs ; there 

 are no areolae or pores (stomata), and the thallus is much thin- 

 ner than in the Liverworts, in some species consisting of only 

 a single layer of cells except at the midrib. The capsules are 

 borne singly on setae arising directly from the thallus. They are 

 . spherical to elongated-ovoid and remain enclosed in the calyptra 

 until mature, when the setae rapidly elongate and break open the 

 calyptra which is left at the base of the seta. The capsules open 

 by four valves as in many of the Scale Mosses. A careful 

 search of wet bare earth in shaded or springy places will 

 nearly always yield one or more species of this family. 



KEY TO THE GENERA. 



1 . Thallus with a distinct midrib 2 



Thallus without a distinct midrib 4 



2. Thallus ^ to j 5 inch wide, dichotomously branched, ciliate 



along the margins Metzgeria. 



Thallus YT, to ^ inch wide, not ciliate at margins, entire or 



lobed 3 



3. Thallus simple or only once forked, i to 4 inches long, pros- 

 trate; margins sinuate to entire; capsule ovoid-cylindric. . .Pallavicinia. 

 Thallus dichotomously branched 34 to 1 1 / 2 inches long, often 



densely clustered and ascending, margins lobed; capsules 

 spherical without perianth, appearing buried in the midrib 

 for some time before the ripening of spores (Fig. 88) Blasia* 



4. Thallus pinnately or palmately branched, ^V to ^ inch wide 



(except R. pinguis) , Riccardia. 



Thallus subsimple or dichotomously branched, l / & to 1 A, inch in 



width (Fig. 90) Pcllia. 



