265 
of licliens on the trees is certainly not desirable even if not positively 
objectionable. 
It should be noted that the lichens live not only on the rough exfoli¬ 
ating bark of the trunk and larger limbs, but on the smooth growing- 
bark of the smaller bi anches. In fact the smooth branches seem to have 
considerably more on them than the old trunks. The fruticose forms 
are firmly attached to the smooth bark by a small, expanded, disk-like 
portion of the tliallus. The crustaceous forms grow tightly appressed 
to the bark, or, according to Tuckerman,* the lowest forms grow beneath 
the outermost layers of the cells of the bark. We see how closely the 
lichen structure is united to its supporting bark. If not in actual con¬ 
tact it is separated from the green, living bark cells only by an ex¬ 
ceedingly thin layer of cork three or four cells deep and not thicker than 
tissue paper. Furthermore, many species seem to be restricted to the 
smooth bark. It seems highly probably then that lichens which are in 
such close connection with the living bark and are more or less restricted 
to it, take something from the tree. Possibly this consists only of some 
essential mineral matters, but perhaps also of elaborated sap, and even 
if they take nothing from the trees their presence may seriously inter¬ 
fere with the functions of the bark. 
The Bartlett pear orchard above mentioned lias been planted about 
seventeen or eighteen years. The trees were headed low, and allowed 
to grow as low, pyramidal standards. Many of the trees had their 
branches completely fringed with lichens (see Plate xxx). Where 
the fruticose and foliaceous forms did not cover the limbs the spaces 
were filled with the crnstaceous species. The fringe-like and foliaceous 
forms are more conspicuous, but the crustaceous forms are probably 
more injurious. 
I am inclined to think that lichens, when abundant, do considerable 
injury to the trees, although it is hard to get any positive evidence 
to bear out this belief. The badly infested trees occur in this 
orchard in patches of several acres in extent, although almost any¬ 
where on the 200 acres the trees were found carrying more or less of 
the crustaceous forms, if not the larger growths. The crust-like lichens 
give to the normally smooth yellow bark a grayish, dappled, or spotted 
appearance, noticeable from a distance. 
EXPERIMENTS WITH BORDEAUX MIXTURE. 
I x 
A block 10 trees square, containing in all about 80 trees, was 
severely pruned back, the whole top of each tree being removed, leav¬ 
ing only the body and main limbs. This severe treatment and the 
washing described below were directed primarily against a twig disease, 
which will be reported on at another time. The object was to remove 
the twigs and small branches and then to disinfect the remaining parts 
of the tree of all fungi, lichens, etc. 
^Synopsis of Noitli American lichens, p. vill. 
