1904] PINK-——A- LICHEN SOCIETY 267 
laid and more exposed rocks of the riprap have weathered consider- 
ably and differentially, the rate of weathering depending partly upon 
position and in part upon the amount of cementing iron contained 
in each particular piece. In its position away from running water, 
a portion of the disintegrating sand of the riprap remains on the ground 
and in the crevices and forms a small amount of soil upon which 
plants may grow. Again the riprap is partly swamp-bound, with 
woods some 150" away. Also there are only two or three bowlders 
near by, the Kansan drift which covers the surrounding country 
carrying very few at the surface. Thus there are at present and have 
been since the establishment of the society no lichens, or at least none 
that can be detected readily, in the region immediately surrounding 
the society; for one would hardly look for lichens among the plants 
of the grass-sedge swamp or among the xerophytic spermatophytes 
of a gravelly railroad bed worked year after year. Hence we have 
here an isolated lichen society, which has developed to its present 
condition during the last thirty years, while separated from the nearest 
society by 150™, 
How each individual species of the society found its way to the 
Spot cannot now be ascertained certainly. Indeed, one well acquainted 
with lichens might pass the spot without examination, so complete 
is the isolation of the society and so barren do the rocks appear at first 
pection. In fact it is only after an examination of the rocks with 
ahand lens and a careful survey of the crevices that anything of special 
i iS discovered. Till recently cut, a group of oaks and other 
ea — Standing about 150™ distant from the riprap, and these 
fi foliose Parmelias and Physcias, the fruiticose Ramalinas, 
Ag lg Placodiums, Lecanoras, and Rinodinas. But the 
a foot in . ng when cut, the largest measuring scarcely more than 
a. oe and the majority about half this size, and were 
ese liche ‘when the riprap was made, surely not carrying any of 
trees of ae Pept perhaps some of the crustose forms. Were 
society : as and bearing lichens immediately surrounding the 
hee Je from the trees would now be gaining a foothold 
ities . > though not so well adapted to the substratum 
another r ichens. Were numerous bowlders near at hand, 
"ye of lichens might now be less sparingly represented in the 
