120 
THE DICTIONARY OF GARDENING, i 
Phytophthora—continued. 
the first true leaves before the disease forms spots on 
the stems and on the various leaves. In damp weather, 
the diseased parts soon rot; in dry weather, they become 
5 dry and brown. All the diseased parts are penetrated by 
Fic, 142. PHYTOPHTHORA INFESTANS—a, Entire Conidiophore, and 
base of a second, coming through a stoma of the leaf; on the 
branches are several Conidia (the thicker parts show the 
successive tips on which Conidia are 2 in the var 
characteristic of the genus Phytophthora); b, Conidium, wi 
ave Zoospores inside it; c, Free 33 with two Cilia; 
, Zoospore, after settling down; e, Zoospore, emitting Myce. 
rag a is magnified about 80 times ; the remainder about 400 
times. 
the threads of the Fungus; and numerous conidiophores, 
aʒare pushed ont through the skin of the stem or leaf. The 
. ‘pestle if they fall into dewdrops, emit one or more 
anew. The damage * 9 very N The 
Fungus is propagated in the following spring by means 
of the resting spores. These are produced as in Perono- 
spora, and are formed in the diseased tissues. When 
the latter decay, the spores are scattered in the soil, 
there to remain till the warmth of the following spring 
promotes their germination. If a suitable host is at 
hand, the Fungus bores into it, and runs the same course 
as before. It has been found, experimentally, that 
resting spores can retain their capacity for germinating 
even for four years. Seed-beds of forest-trees of the 
species liable to injury should be established in places 
free from shade, and airy, to allow of free evaporation 
of superfluous moisture. All dead or dying plants should 
be at once picked out and burned. The seedlings must 
not be crowded. Ground where a diseased seed-bed has 
stood must not be used for making a new bed for some 
time, lest disease should break out afresh from ger- 
minating resting spores left in the soil, thus perpetuating 
the evil. 
The Potato-disease Fungus (P. infestans) is one of the 
most hurtful of all Fungi, because of the damage it 
inflicts on the Potato crop; in some years, a half, or 
more, of the yield is destroyed. In the year 1845, the 
disease produced by this Fungus first came prominently 
into notice, since, in that year, it spread over the West 
of Europe, including Britain and Ireland, and over the 
en Ce ee In the latter half 
each producing two, or less often three, egg-shaped conidia, 
threads, or 3 produce a number of “ swarm- 
Phytophthora—continued. 
of August, the crop in our own country was blighted, 
causing heavy losses to farmers; while severe and fatal 
famine and disease followed in Ireland. In years pre- 
vious to 1845, the disease of Potatoes had been 
observed occasionally in various places; but, since 1845, 
it has never been wholly absent from any country 
where it has once appeared, though it is much more 
destructive in some years than in others. The Fungus’ 
attacks several plants belonging to the same order as 
the Potato (Solanacee), such as the Bitter-sweet (Sola- 
num Dulcamara), Schizanthus, and the Tomato (Lyco- 
persicum esculentum). The damage done by it to the 
latter plant is sometimes considerable. Occasionally, 
it grows on plants of the order Scrophularinee. The 
appearance of the diseased Potato-plants is too well 
known to require a long description. On the leaves 
FIG. 143. Poraro-tear ATTACKED BY PHYTOPHTHORA INFESTANS, 
in the dark spots, k, x, k. 
brown spots appear (see Fig. 143), rapidly extending, and 
becoming rotten towards the centre. The lower surface 
of the spot bears a thin, whitish coating, seen most dis- 
tinctly on a watery-looking, discoloured border round 
the spot. This whitish coat consists of numerous conidio- 
phores, emerging from the stomata in small groups. 
Each has a few branches, with conidia near the tips 
(see Fig. 142). The tissues of the leaf are full of the 
mycelium of the Fungus, pushed between, and lying in 
contact with, the cells of the leaf, and causing them to 
rot. Zoospores are formed in the conidia in water (e.g., a 
dewdrop), asdescribed under Peronospora (which see). 
They are set free by the conidium bursting, and each 
moves, by means of two fine hairs (see Fig. 142, c) in the 
water on the leaf. Each settles down after a little while, 
and emits (see Fig. 142, e) mycelium, which, ina short time, 
penetrates the leaf, and gives rise in it to a new diseased 
spot. Any movement of the diseased plants, by wind or 
otherwise, however slight, is sufficient to spread the 
conidia all round; and thus, from a single plant, a 
whole field may be infected in a very short time. But 
the whole plant becomes filled with the mycelium, alike 
in leaves, stems, and branches ; and the tubers also 
become infected, both in this way, and by the entrance 
of mycelium tubes emitted by zoospores, washed down 
upon them if they lie near the surface of the soil. In 
whatever way the mycelium reaches the tuber, the latter 
becomes rotten, in patches or entirely; and, on careful 
