456 



METZGEEIACEAE. 



3. PAIiLAVICINIA S. F. Gray. 



Thallus pale to dark green, forking or with ventral adventive branches, 

 consisting of a thickened median portion, or midrib, with a central strand of 

 elongated cells and two broad lateral wings one cell thick except toward the 

 midrib; unicellular hairs lacking and margin entire. Antheridia in an 

 elongated median group, protected by imbricated toothed scales. Archegonia 



in a circular median cluster, surrounded by 

 variously toothed and more or less coalescent 

 scales. Pseudoperianth tubular, ciliate or 

 lacerate at the mouth. Capsule elongated, 

 oval, the wall splitting into from two to four 

 valves, two to six cells thick; ring-like thick- 

 enings none. Elaters with two or three bands 

 of thickening, free from the valves. [Probably 

 in honor of Ji. Pallavicini, Archbishop of 

 Genoa.] About 25 species, mostly tropical 

 and subtropical. The following typical. 



1. Pallavicinia Lyellii (Hook.) S. F. 

 Gray. Lyell's Pallavicinia. (Fig. 502.) 

 Growing in irregular mats or scattered among 

 other plants. Thallus almost always with 

 ventral branches rapidly broadening out from 

 a stalk-like base, mostly 2"-2J" wide and 10"- 

 20" long, flat or slightly crispate along the 

 margins; inflorescence dioecious; spores mostly 

 20-24 /x in diameter, the surface finely reticu- 

 lated. [Jungej-mannia Lyellii Hook.] 



On moist soil, sometimes submersed. Devon- 

 shire and Paget Marshes. Widely distributed, 

 especially in tropical regions. 



Family 2. JUNGERMANNIACEAE. 



JuXGERilAXXIA FaMILY. 



Plant body usually prostrate or ascending, dorsiventral ; branches 

 lateral or ventral; leaves normally in three longitudinal ranks, two dorsal 

 or lateral and one ventral, those of the ventral rank (the underleaves) 

 smaller than the others and sometimes absent altogether. Antheridia borne 

 singly or in small groups in the axils of more or less specialized leaves, 

 the perigonial bracts. Archegonia borne singly or in groups at the tips 

 of branches, surrounded by specialized leaves, the perichaetial bracts and 

 bracteoles. Perianth present in many genera, consisting of a cylindrical 

 or prismatic tube open at the apex. Capsule spherical to cylindrical. 

 About 150 genera and some 4000 species, widely distributed, most abun- 

 dant in tropical regions. 



A. Leaves plane or nearly so, undivided or more or less deeply bifid with broad lobes, 

 1. Leaves succubous. 

 Leaves undivided. 



Leaves ciliate. 1. Plagiochila. 



Leaves entire. 4. Odontoschisma. 



