AN ENCYCLOPAEDIA OF HORTICULTURE. 121 
Phytophthora—continued. 
examination, the starch grains are found to be dissolved 
and fissured. + Where the tuber has not passed beyond 
the first stage of disease, it shows little sign of injury 
externally; and such tubers are often used for planting 
for next year’s crop, with the frequent result of diseased 
plants growing from them. So far it may be said that 
all mycologists are agreed in regard to the development 
of this Fungus; but what remains to be stated here is 
still hotly discussed. Globular cells, three or four times 
the diameter of the mycelium, possessing a thick, warty 
outer coat, and a thin inner one, were observed in 
diseased potatoes, even as early as 1845. Mr. W. G. 
Smith has found such bodies very abundantly in old 
potatoes, and in diseased leaves kept in a vessel over 
water (i.e., in moist air); and has observed, in regard 
to them, a process of development like that in Peronospora 
nivea, Ko.; and he asserts that these brown, globular 
cells are the resting-spores of the Potato-disease Fungus, 
This is denied by Prof. De Bary, of Strasbourg, and 
by others. Mr. A. S. Wilson has brought forward a 
theory, with reasons in support of it, connecting with 
the Potato-disease Fungus numerous small, oval bodies 
(that are white by reflected, and dark by transmitted, 
light), which are very abundantly scattered throngh the 
tissues of Potato-leaves, Ko. He and Mr. Smith believe 
that they have traced these small bodies into actual 
connection with the undoubted mycelium of P. infestans. 
The bodies, on analysis, are found to consist largely of 
particles of oxalate of lime, with a basis of protoplasm. 
Mr. Wilson regards them as a resting condition, analogous 
to the sclerotia of other Fungi, e.g., that of Peziza postuma, 
in its uses to the Phytophthora. The true nature of the 
bodies has been hotly discussed in the “ Gardeners’ 
Chronicle during the years 1883-85. Mr. Wilson regards 
Potatoes as almost all infected throughout their tissues 
by these resting masses of the Fungus, which, he con- 
siders, emit mycelium, and give rise to disease, under 
Conditions favourable to the growth of the Fungus. 
Much has been written on remedies for the Potato disease ; 
yet it can hardly be said that any methods have 
been discovered really efficient in securing the Potato 
orop against this scourge. Beyond doubt, the unnatural 
conditions induced by continuous cultivation and pro- 
pagation from the tubers, have rendered the plants a 
more easy prey to the Fungus, and more liable to suffer 
severely from its attacks, than uncultivated plants would 
be; and this is seen if the effects on the Potato are 
contrasted with those on the Bitter-sweet, a plant also 
occasionally attacked by the Fungus. Prevention is best 
promoted by selecting, as seed tubers, varieties known 
to resist disease, since some are much hardier than 
others in this respect. The soil should be well drained, 
and there should be free circulation of air around the 
plants, to promote evaporation, since moisture, confined 
air, and warmth, promote the rapid growth of the Fungus. 
The seed tubers should be planted uneut, or the cut 
surfaces should be allowed to heal, or may be seared 
with a hot iron, or otherwise coated over, before being 
put into the soil. All tubers that show traces of disease, 
and all dead stalks, leaves, K., should be burned, to 
prevent the propagation of the disease through them. 
Of recent years, Mr. Jensen, of Copenhagen, has strongly 
advocated “ protective moulding,” and his views have been 
stated and supported at some length by Mr. C. B. 
Plowright, in the Gardeners’ Chronicle.” The system 
was also suggested by Dr. Lang, in 1858; but it has not 
been generally adopted. Mr. Jensen’s method may be 
briefly summarised as follows: The ground should be 
thoronghly worked and quite friable, and the potatoes 
should be planted in rows about 30in. apart. The first 
moulding should be about Ain. high, and flat on top. The 
protective moulding should be done as soon as diseased 
Spots appear on the plants, and, in any case, should not 
VoL III. 
| 
Phytophthora—continued. 
on a large scale, in fields, by a engg garm lough, 
The layer of earth should be, when it 4 
not less than 4in, thick along each side of the row, above 
the tubers. At the same time, the tops should be 
bent over to one side of the row, and allowed to wither; 
and they may then be cut off and removed, The tubers 
may be lifted in about a week after the removal of the 
tops. This system proceeds on the belief that the tubers 
are infected by conidia and zoospores washed by showers 
from the leaves and through the soil on to the tubers, 
and not by mycelium through the stalk. Mr. Jensen 
also recommends disinfecting the seed tubers by storing 
them for four or five hours in a dry-air chamber, at 
a temperature of from 100deg. to 105deg. Fahr. Of 
course, other host-plants of the Fungus, whether wild or 
cultivated, ought not to be grown in the neighbourhood 
of Potatoes. Attempts have been made to substitute 
some other species of tuber-forming Solanum for S. tube» 
rosum, but without great success. The most promising 
seem to be 8. Commersoni and S. Maglia, the former of 
which appears to be uninjured by P. infestans. 
PHYTOPTUS. See Mites. 
(of Sprengel). A synonym of Sphacele 
(which see). 
PIARANTHUS (from piaros, fat, and anthos, a 
flower; alluding to the shape of the blossoms). Orp. 
Asclepiadew, A genus comprising, perhaps, half-a-dozen 
species of greenhouse succulents, with low, deeply four- 
jointed stems, natives of South Africa. Flowers mediocre, 
often fasciculate; calyx small, five-parted; corolla cam- 
panulate, deeply five-cut, the lobes narrow, acuminate, 
valvate; corona lobes five, inflexed. The species have 
the general habit of Stapelia (which see for culture). 
P. us (dark-flowered), f. three or four r; corolla dark 
perl, the segments lanceolate, silky — j August. 
ranches usually hexagonal, erect ; 5 a little sinuated, 
having strong, spreading teeth. A, bin. 1774. (B. M. 1648.) 
P. geminatus (twin). The correct name of plant described in 
work as Podanthes geminata, 
PICEA (from piz, pitch; the trees produce abundance 
of resin), Silver Fir. Syn. Abies (of Don). Including 
Veitchia, ORD. Conifera. A genus comprising about a 
dozen species of mostly hardy, evergreen trees, inhabit- 
ing the extra- tropical regions of the Northern hemisphere. 
Flowers monewcious, Leaves acicular, spirally scattered, 
with the midrib prominently quadrigonal or sub-terete, 
contracted into a very short, articulated, persistent petiole. 
Cones ovoid or oblong-eylindrical, erect or horizontally 
spreading; the bracts not falling away from the axis at 
maturity, as in Abies. Owing to a snecession of blunders 
in works treating on Conifers, the generic names Abier 
and Picea are generally transposed. For culture, «¢ 
i h ellowinn 
„ ajanensis (Ajona). shoots glabrous when young, 
3 — marked Jona) oblong, — inent. cushions, L, 
those on the side shoots in many rows, but twisted at the base 
so as to be all in the same horizontal plane; on the upper 
surface of the branch appressed, parallel in direction to the 
branch; all flattish, linear-oblong, rather obtuse, not spine- 
tipped; upper surface three-ribbed; underneath, one-ribbed, 
cones erect, lin. to An. long, An. broad, oblong, tapering to 
each end; scales shining-brown, oblong-ovate, A. Toft. to Bolt. 
Japan, 1861. A beautiful Fir, resembling P. exeelea, but more 
elegant. Syn. Abies Alcoquiana, of gardens. (B. M. 6743; G. C. 
n. S xviii, 183.) p i 
. te!“ White Spruce, young shoots very glaucous. 
4l Se longer, and more pointed than in other species, 
somewhat glaucous, scattered around the branches, erect, quad- 
rangular. cones oblong-cylindrical, light brown, small when 
ripe; scales loose and thin, round or bluntly pointed, with en- 
tire edges. A. Dit. to Wit. Canada, &c., 1700. (F. d. 8. 
2251.) 
2 8 Alcock' e).“ young shoots covered with , weak 
"o 4 — the leader shoots appressed ; on 1 — 
given off on all sides; all rigid, more or less curved, linear- 
R 
3 
