7O 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 i, 1902. 



Family VERRUCARIACE^E. 



PYRENULA. 

 i. 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 t ....fulva. 



Thallus brownish or blackish. 



Thallus breaking up into small areolaB .fuscella . 



Apothecia entirely immersed, level with the surface of the 



thallus mucosa. 



Apothecia elevated above the surface of the thallus maura. 



