KITCHEN-GARDEN 
If the brown spots on the under side of the 
leaf are examined with a pocket lens, numbers 
of delicate white threads will be seen, especially 
towards the circumference of the diseased patch. 
Higher magnification reveals that these delicate 
threads are simple or branched conidiophores, 
which originate from the mycelium of the 
fungus, ramifying the tissues of the leaf, and 
emerge singly, or most frequently in small 
clusters, through the stomata of the leaf, for 
the purpose of producing conidia on the surface 
of the leaf, whence they are readily dispersed 
by wind, rain, passing animals, &c. The 
conidia are egg-shaped and colourless, and are 
produced at the tips of the conidiophores; but 
when a conidium is once formed, the branch or 
VEGETABLES. 499 
Preventive means are—Spraying the growing 
haulms with Bordeaux mixture, which, apart 
from its action on the fungus, has greatly im- 
proved the yield of tubers. Potatoes obtained 
from a diseased crop should never be used as 
“sets”, on account of the probability, almost 
certainty, of the presence of the mycelium in 
the tubers. Diseased stems, leaves, and tubers 
should not be allowed to lie and rot on the 
ground, neither should they be thrown into the 
piggery nor on the manure-heap; burning is 
the most effectual method. The disease is most 
severe where Potatoes are grown in a low damp 
district. 
Although all known varieties of Potato are 
susceptible to the disease, some are much more 
axis bearing it continues to elongate in the | so than others, and endeavours should be made 
same straight line, leaving 
the conidium apparently 
attached to its side. After 
the branch has grown for 
some time, a second coni- 
dium is produced at its tip, 
to be again left behind by 
the continued growth of 
the branch above it. 
This peculiar mode of 
reproduction is the only 
constant feature that dis- 
tinguishes the genus Phy- 
tophthora trom Peronospora. 
The conidia give origin 
to a number of zoospores 
when placed in a drop of 
water, or on a damp sur- 
face, 2S that of a leaf 
covered with dew. The 
zoospores move about actively for some time in 
the water, and finally settle down and emit a 
slender germ-tube, which enters the tissue of a 
leaf through a stoma, or bores directly through 
the epidermis. 
Conidia that are washed by rain upon young 
tubers of the Potato that are exposed, produce 
zoospores, and these infect the young tuber, 
entering its tissues and forming a mycelium. 
The mycelium of the fungus also passes down 
diseased stems of the Potato, and thus infects 
the tubers, the mycelium either passing into 
a latent condition until the following season, 
when it renews its activity and grows along 
with the stems springing from the tuber; or it 
continues to grow after the Potatoes are stored, 
especially if “sweating” takes place, and in this 
manner frequently spreads rapidly through the 
mass of tubers huddled together. 
Fig. 1260.—Unsprayed and Sprayed Potato Plots. 
| to secure those varieties least susceptible to the 
disease in a given district. (G. MASSEE, in 
Plant Diseases.) 
Mr. Sutton wrote: “I must not conclude with- 
out referring to the use of the Bordeaux Mixture 
as an application for preventing Potato disease. 
Fig. 1260 shows two plots of Magnum Bonum 
Potato growing side by side during the past 
season; that on the right-hand side having 
been sprayed three times, and that on the left- 
hand not having been sprayed at all. It will 
be seen that the effect was very marked. The 
growth of the sprayed plants continued some 
time after the unsprayed portion had died down. 
The weights of the two plots when lifted were 
as follows:—The sprayed, 3 cwts., 1 quarter, 
25 lbs., and the unsprayed, 3 ewts., 1 quarter, 
4 lbs. Strange to say, the quantity of diseased 
tubers was precisely the same in both plots, viz 
