Josselyn Botanical Society 



15 



The tree, an elm, grew by the roadside and had no imme- 

 diate neighbor, large or small. It was, in fact, such a tree as 

 a lichenologist delights in, because of the ecological problems 

 presented. The most conspicuous lichen on our tree trunk 

 was Panne Ha cape rata. This plant, a Linnaean species, is 

 presented under its time-honored name, and not the one pro- 

 posed by that group of lichenologists who call themselves 

 advanced, but whose advancement consists principally of an 

 ardent ripping up of traditions and the establishment of an 

 infinity of new combinations. The lichen, an exceedingly 

 common one, was observed to be growing on the easterly, 

 northerly and southerly sides of the trunk, and one great 

 patch more than two feet in diameter was conspicuous and 

 recognizable from a distance. All of the plants were without 

 apothecia — in fact, the species is seldom found in a fertile 

 condition — and represented that phase in which the whole 

 surface of the thallus is covered with granular soredia. Such 

 conditions of the plant are assumed to be old or aged exhibits, 

 and are explained by an observed tendency of the species 

 when found in similar habitats to discontinue growth by cen- 

 tral innovation. Growth in lichens persists throughout the 

 whole vegetative tract, and in those species whose physiology 

 forbids growth by central innovation, activity continues, but 

 in a vertical direction, and in the form of soredia. 



Second to Parmelia caperata in abundance was Xantho- 

 ria parietina. This plant is described under the generic 

 name of Theloschistes in Tuckerman's Synopsis, and corre- 

 lated with Physcia by Nylander. The plant is that orange- 

 colored thing so common and conspicuous on roadside trees 

 and walls. The coloring matter in this lichen is chrysophanic 

 acid, present in little crystals in the cortex. Why this sub- 

 stance should be present in and color the thallus of Xantho- 

 ma parietina and some allied lichens, yet be entirely deficient 

 in other orange-colored species, has never been explained. 

 The peculiar fact may be noted that the species, when grow- 

 ing in shaded places, is often found of an ashy or gray color 

 with the exception of the apothecia, these having a more or 

 less normal coloration. In very damp habitats the thallus is 

 decidedly green and the apothecia less orange than is com- 

 mon. In particularly exposed and arid situations, as on the 



