4 A. W. Evans — North American Species of Frullania. 



to the keels, and the perianth which results is triangular in section 

 with a postical keel corresponding with the folded underleaf. This 

 is the hypogonianthous type. In case no underleaf takes part in the 

 formation of the perianth, the other two anthophylls unite postically 

 and give rise to a perianth which is flattened, either laterally as in 

 Plagiochila or antico-postically as in Radula. The typical charac- 

 ter of the perianth of Frullania is often obscured by the interposition 

 of supplementary keels or ridges. 



A much less extensive coalescence is sometimes to be found in the 

 involucre, where a bracteole may be connate on one or on both sides 

 with the corresponding bracts. In several of our species the degree 

 of such coalescence is by no means constant and it is only occasion- 

 ally to be relied on as a specific character. In F. Bolanderi, for 

 example, the bracteole may be connate on both sides or on only one 

 side ; in F. Kunzei, it may be connate on one side or entirely free ; 

 while, in F. Virginica, all three conditions may be found. 



The inflorescence of Frullania is a character of great importance 

 and should be determined wherever possible. The sporophyte, on 

 the contrary, which is usually difticult to obtain and very uniform in 

 structure, is of little value in distinguishing species and is not made 

 use of in the following descriptions. 



Frullania attains its greatest develoijment in the tropics, where it 

 is represented by numerous species in both hemispheres. In 1884, 

 Spruce' divided it into six subgenera, several of which are typically 

 tropical. Five of these subgenera are represented in our flora, 

 one being confined to Florida. Some of Spruce's subgenera are 

 connected by intermediate species and it is impossible to draw 

 rigid lines of distinction between them ; still, they are for the most 

 part natural assemblages of forms and are very convenient and useful. 

 In Europe, eight species of Frullania have been recorded, three of 

 them belonging to the subgenus Trachycolea and the others to Thiop- 

 siella. Only one of these species, F. Tatnarisci, has been certainly 

 found in North America, although two others have been accredited 

 to us. A striking peculiarity of our FridlanicB is the large number 

 of monoicous species among them ; no fewer than nine exhibit this 

 character, while the eight European species ai-e all dioicous. 



Key to our Subgenera. 

 Lobule inflated in the upper part only, connected with the lobe by a 

 long fold subparallel with the stem ; inflorescence paroicous ; 

 perianth trapezoidal in section. Subgenus I. Chonanthelia. 



' Hep. Amaz. et And., 7. 



