112 Disease of Olive and Orange Trees, By W. G. Farlow. 
correspondence has not been sufficiently extensive or minnte to 
enable us to give any statistics of the ravages of the disease, 
to ascertain the climatic or other changes v^hich have preceded 
or accompanied the breaking out of the epidemic, or to decide 
whether it is the same form of disease v^hich has been reported 
to occur in Florida. Our specimens present the disease as it 
appears when in a somewhat advanced stage, and after the leaves 
and stems have become so changed as to attract attention. 
Mycelium. — The leaves of the olives which are affected by 
the disease are somewhat curled and shrivelled, and are of a 
browner colour than normal leaves which have been gathered 
but a few weeks. On both surfaces of specimens sent us are 
black spots of greater or less extent, but in no case is the leaf 
perfectly black. On the upper surface the black spots are more 
numerous, more distinct in outline, and harder in substance, 
than on the lower, where they were more diffuse and of a pow- 
dery consistence. The twigs, of which we received only small 
specimens, are covered with spots which resemble more closely 
those on the upper than on the lower surface of the leaves. In 
one specimen the spots are nearly confluent, and the bark is 
visible in only a few places. After the leaves or stems have 
been soaked in water for a short time, the black substance can 
be scraped off without the least trouble, leaving the bark tole- 
rably clean. The black substance, when seen with a magnifying 
power of four hundred diameters, is found to be composed of 
the stellate hairs peculiar to the olive, over which is growing 
a fungus, to the dark colour of whose mycelium the spots owe 
their colour. The mycelium is very variable in appearance. As 
a rule, it is composed of monihform hyphge, whose cells are '006 
.mm. by '008 mm., and in some places almost spherical. The 
colour of the cell-wall is a dark or purphsh brown, and in most 
of the cells there is a comparatively large-sized oil- globule. 
These hyphae branch in all directions, and the cells of the 
branches grow constantly longer, narrower, and paler, although 
in all cases retaining a tinge of brown. The relation of the 
mycelium to the stellate hairs and outer part of the twigs and 
leaves is clearly seen in cross sections. The hyphse run along 
the surface of the epidermis and of the hairs, which it will be 
remembered resemble a broadly-opened, short-handled parasol. 
They are twined closely round the stems of the hairs, so closely, 
that the fungus cannot be removed without tearing them off. 
They do not enter into the cells of the olive, and there are no 
haustoria as in the case of some of the leaf parasites belonging 
to the Erysi^phei. Occasionally there are little knob-like projec- 
tions of the cells which seem to indicate haustoria; but by the 
most careful examination which we have been able to make, we 
