35 



Fruits are not uncommon, usually renewed every summer, 

 maturing in autumn. The special, narrow lobes spring upward from 

 the tips, at first curling to form a hood over the young fruits. Later 

 the fruits become flat on the upper surface of their lobes, and often 

 finally roll into a cone with the chestnut-brown or blackening fruit- 

 ing surface outward. Spores when mature, colorless, 4- to 8-celled, 

 extremely variable in size, but usually 40 to 70 by 3 to 5 microns. 



Peltigera canina when fruiting will hardly be confused with 

 any other lichen except its own subspecies, which may be ignored, 

 or separated as indicated in following paragraphs. From P. 

 aphthosa, a distinct species, it may be distinguished by the color, 

 remaining brown, gray or dark olive green when wet ; also by the 

 absence of peculiar small, fruit-like bodies scattered over the upper 

 surface, described under that species. P. aphthosa and P. venosa 

 have the algal cells Protococcus. From species of Sticta and 

 Nephroma, it can be separated by the thickened veins, though there 

 are forms of the subspecies P. malacea in which the brown veins 

 are so closely interlaced that they seem to lose their identity, and 

 the pale spaces between them appear like the speckling of a Sticta. 

 These rare forms cannot be determined surely unless fruits are 

 present. Associated with Peltigera canina along stream beds will be 

 found Dermatocarpon aquaticum (Group 12), smaller in its parts, 

 and turning rather bright green when wet. In texture it is rather 

 leathery, but there are no thickened veins beneath. Hydrothyria 

 venosa ( Group 1 1 ) , a blackish lichen often found under water, has 

 veins beneath, but is thin and delicate, and gelatinous looking when 

 wet. Leptogiiim saturninum, a slate-gray gelatinous lichen of Group 

 11, is clothed on the under surface with a nap of rather long, fine 

 hairs, but has no veins. Few other lichens could cause confusion, 

 especially as the larger forms are the largest of all our papery 

 lichens. 



The subspecies of Peltigera canina are unsatisfactory and in- 

 constant in their characters, but are here briefly described for those 

 who wish to study them. 



Peltigera horisontalis is a subspecies with shortened fruit-lobes, 

 often so short that the fruits appear to rest on the pointed tips 

 rather than on special lobes. They are flat, broader than long, and 

 held in a more or less horizontal position, instead of pointing up- 



