7 o 
CUMMINGS 
tion of the species, as well as structural characteristics. One 
element which has added to the difficulty of determination is 
the frequency with which different genera and species were 
found growing together, one small fragment of rock, not more 
than an inch square, showing often four distinct species, some¬ 
times as many genera. The commingling of earth forms, 
which is so common a characteristic of northern lichens, is also 
noticeable. 
I would acknowledge my great indebtedness to Dr. Farlow 
for the free use of the Tuckerman Herbarium of Lichens, 
without which I should have found it impossible to do this work, 
as well as for many other courtesies ; to Dr. Trelease of the 
Missouri Botanical Garden, and Miss Day of the Gray Her¬ 
barium, for assistance in finding the literature of the subject; 
and to Miss Maude Metcalf, graduate student of Wellesley Col¬ 
lege, for her kindness in making the drawings. 
This paper was presented in part before the Society for Plant 
Morphology and Physiology at its meeting held at Columbia 
University December 31, 1901, and January 1, 1902. 
Family VERRUCARIACEiE. 
PYRENULA. 
1. Pyrenula gemmata (Ach.) Naeg. & Hepp. 
Verrucaria gemmata Acharius, Meth. Lich. 120. 1803. 
Pyrenula gemmata Naegeli & Hepp, Flecht. Eur. no. 104. 
Disenchantment Bay (Trelease, 803^, 821, 842 in part, 1170 in 
part). On bark of shrubs, associated with Buellia. New to Alaska. 
Common in New England, according to Tuckerman, but no other 
American localities are given in his Synopsis. 
VERRUCARIA. 
KEY to the species. 
Thallus obsolete. thelodes. 
Thallus evident. 
Thallus yellowish-white, margining the apothecium..... .fulva. 
Thallus brownish or blackish. 
Thallus breaking up into small areolae. .fuscella. 
Apothecia entirely immersed, level with the surface of the 
thallus. mucosa. 
Apothecia elevated above the surface of the thallus. ?naura. 
