Jfig. 7.
V E R R U C A R I A biformis.
Deceptive Verrucaria.
CRYPTOGAMIA Lichenes.
Gen. Char. Tubercles of a different substance from
the thallus, simple, convex, not expanding, but
furnished with a central pore, and inclosing a
somewhat gelatinous nucleus.
Spec. Char. Crust indeterminate, filmy, continuous,
or sparingly cracked, slightly rugose, or smooth,
or somewhat powdery, greyish. Tubercles small,
prominent, hemispherical, invested with a thin
film.
J%fOT uncommon, but easily overlooked, on young oaks ;
sometimes found on ash and other trees.
On smooth bark the crust forms irregular patches, seldom
two inches in width, indeterminate, or, if several plants are
crowded together, edged with a black line, of a very thin,
polished, smooth, or minutely rugged film, sometimes inclined
to peel of in little scales; its hue pale grey, almost
white when dry, or more or less deeply tinged with olive.
It is not unfrequently suffused, either all over or in part,
with a black granulated or powdery matter which adheres
so closely as not to be removed by rubbing (b). Tubercles
numerous, scarcely half so large as poppy-seed, tolerably
regular in size, orbicular, hemispherical, or rather more
prominent, scarcely either papillose or umbilicated at the
apex, but early marked there with a minute dot, which,
usually, soon becomes an irregular chink, giving to old tubercles
a broken and imperfect appearance, and sometimes
dividing them almost to the base into two or, occasionally,
three portions: their surface is black, often with a brownish
tinge, sometimes polished, but usually minutely granulated,
incrusted in the lower part with a film from the thal-
lus, which in an early stage often invests the whole tuber