54 THE DICTIONARY 
OF GARDENING, 
Pear—continued. 
called peridia, and contain minute, nearly globular, simple 
spores, which escape, when mature, through fine slits in 
the sides of the peridia. This Fungus cannot be called 
common in England, and it has not been recorded from 
Scotland; but in many Continental localities, it is so 
abundant as to do much injury to the trees. 
Fig. 56. PEAR LEAVES ATTACKED BY ROESTELIA CANCELLATA 
(believed to be a stage in the ih se gag of Gymnosporan- 
cone Sabine)—a, Upper Surface, and b, Lower Surface, of 
>. m 9 A on 3 e 9 tga — 
border; p, on Lower Surface, bearin eridia, as de- 
sorfbed in’ the taxt RETT 
Some years ago, the Danish botanist, Oersted, made 
investigations into the development of this Fungus, which 
led him to the result, now very generally accepted by 
botanists, that it is only a stage in the life-history of a 
Fungus which was regarded in former times as entirely 
disconnected with the Roestelia, and which grows on the 
branches of certain species of Juniper, notably of the 
Savin (J. Sabina). This latter Fungus, known as Podi- 
soma fuscum, Cda., or Gymnosporangium fuscum, DC., 
induces a thickened state of the branches of its host. 
From this project numerous cylindrical or bluntly conical 
Fie. 57. JUNIPER TWIG ATTACKED BY GYMNOSPORANGIUM 
FuscUM—c, Outgrowths, in which Spores are formed. 
outgrowths, often jin. to lłin. long (see Fig. 57, c). 
These outgrowths are at first yellow, but become brown; 
and, when moistened, they assume the consistence of 
jelly. The microscope shows that they are made up of 
colourless, one-celled filaments, imbedded in the jelly, 
and running from within outwards, each of which bears at 
its tip a small spore of an elliptical or biconical form 
with a division wall in the middle, so that it is made 
up of two cells, base to base, as in Puccinia. The 
spores lie on the surface of the body, and, when it dries, 
Pear continued. 
they are blown about by the wind. When one germi- 
nates, it forms one or two filaments, made up of a row 
of cells; and from each of the cells, from the tip of this 
for a little way down, a branch grows, and forms on its 
tip a minute sporidium. These are believed, when they 
fall on Pear leaves, to give rise to the Roestelia cancel- 
lata. The spores of this, in turn, are now believed to 
be the cause of the Gymnosporangium, when they fall 
on the proper hosts. This phenomenon of a complex 
cycle, believed to exist, peculiarly well marked, in many 
species of Puccinia, is further referred to under that 
heading. The diseased Pear leaves should be removed 
and destroyed as soon as they show well-marked signs 
of the Fungus, and before the spores are scattered 
from them. The species of Juniperus that nourish Gym- 
nosporangium should not be permitted to grow near 
Pear-trees, especially if the Fungus shows itself on the 
Juniper bushes. 
In August of 1885, a communication was made 
to the American Association for the Advancement of 
Science, by Mr. J. C. Arthur, regarding the cause of the 
disease known as Pear Blight. This disease attacks 
Apple as well as Pear trees, and causes the death of 
the diseased parts. A yellowish, viscid substance is 
formed, apparently at the expense of the starch in the 
branch or other part attacked. Prof. Burrill found that 
the diseased tissues invariably contained a microscopic 
Fungus, named by him Micrococcus amylovorus, belonging 
to the group of Schizomycetes, so prominent of late 
years as the causes of disease in man and in domestic 
animals. Mr. Arthur has made numerous experiments, 
which have convinced him that the Micrococcus is the 
direct cause of Pear Blight. Cure of the disease, after 
it is once established in a branch, seems impossible; 
but prevention of its spread should be aimed at, by the 
removal and burning of all parts that show any signs of 
the disease. Infection of healthy plants is easily accom- 
plished if cracks or wounds on their surface are brought 
into contact with any of the diseased tissues. 
“Cracking” in Pears, and in Apples, may be due to 
more than one cause; but one of the worst forms is the 
work of a Fungus, which, on Pears, has been called 
Fusicladium pyrinum, Fckl., but is now generally re- 
ferred, as a variety, to F. dendriticum, Fckl., now more 
often called Cladosporium dendriticum, Wallr., which, 
in its typical state, grows on Apples. This Fungus grows 
on the leaves and young twigs, and also on all parts of 
the flowers, often preventing the fruits from setting; 
and if they do set, they are crippled and injured in 
growth, and are rendered of little value by the Cracking 
of the skin of the fruit as it ripens. On the leaves, the 
Fungus gives rise to black spots, from }in. to }in. across, 
branching from the centre like a minute tree, whence 
the name dendriticwm, or tree-like. On the fruit, it gives 
rise to similar spots, which very soon become irregularly 
rounded, with a narrow, white margin, surrounding a 
depressed black spot. Around the white margin there 
is a dark border, due to the spreading mycelium of the 
Fungus. On examining the spots with a low magnifying 
power, it is evident that the margin is the edge of the 
epidermis or skin of the fruit, and that the dark, de- 
pressed spot is occupied with a mass of minute bodies. 
On using a lens of higher power, it is seen that these 
bodies are the ends of club-shaped or narrowly-ovate, 
brown spores, or conidia, which are fixed by the narrow 
end to the tip and sides of erect, short stalks. The 
conidia are simple, or are occasionally two-celled. The 
stalks are produced on the surface of a mass or stroma 
of closely-packed small cells, formed by division of the 
threads of the mycelium by cross walls. The mycelium 
does not penetrate far into the fruit. It remains alm 
wholly in the cells of the epidermis, and between them 
and the next layer; though a few branch-threads are 
