AN ENCYCLOPADIA 
OF HORTICULTURE. 207 
Potato—continued. 
unchanged, but the following summer there grow, from 
those lying on or under the soil, from one to three 
Pezize, which have very long, slender, twisted stalks, each 
of which ends in a cup, which very soon becomes flat on 
top, and may reach ŝin. across (see Fig. 257). The upper 
surface bears the very numerous asci standing side by 
sidé ; each ascus incloses eight smooth, oval spores, which 
are ejected from it if the air is at all dry. If the spores 
fall on a suitable food-plant, they reproduce the Fungus. 
All Potato haulms, and other rubbish, should be burned, 
instead of being left to infect the crop of next year. 
Deep ploughing or digging would bury the sclerotia too 
deep to allow the Peziza cups to reach the surface of the 
soil, 
Potato Curl is a puzzling disease, since no evident 
cause could be detected by some observers, while Fungi 
have been discovered by others in the diseased plants, 
It was first observed in England in 1764, and soon after- 
wards was noticed in Rhenish-Germany and elsewhere. 
It has become less hurtful since 1820, or thereabouts. 
The young stems and leaves curve or curl up; the whole 
plant becomes sickly and stunted, and extremely brittle ; 
the stems branch little, if at all; the leaves are small, 
and almost sessile; and the flowers and fruit often fall 
off prematurely, and all the green parts become mottled. 
Tubers are either not produced, or they are very small, 
and so watery as to be unfit for food. If used as seed 
potatoes, the disease usually, if not always, appears in ~ 
the plants grown from them. Careful microscopic exami- 
nation of the diseased plants has led to very different 
conclusions as to the cause, some observers (e.g., Kiihn) 
failing to detect any trace of Fungi, while others (e.g., 
Hallier and Reinke) have found them in the interior of 
the diseased tissues. Hallier asserts, and Reinke agrees 
with him, that the disease is hereditary, or that diseased . 
tubers produce diseased plants, and that these plants are 
not capable of forming tubers ; that mycelium of Fungi 
is present in the inner tissues of the plants; and that 
infection with this mycelium will produce the same 
disease in previously healthy plants. Reinke and Bert- 
hold give the following account of the disease. The 
mycelium is present, they say, in the woody bundles of 
plants as soon as they begin to wither, and in badly- 
affected plants it may be traced throughout from the 
roots to tips of the leaf-stalks. It may also often be 
found in plants that show no outward sign of disease. If 
the plants are kept in a damp atmosphere, their whole 
surface becomes covered with a white coat of conidio- 
phores, or spore-bearers, of Fungi, pushed out from the 
mycelium through the epidermis. These are, at first, 
colourless; and each bears two or three circles of short 
branches at the ends of the cells, which, in a single 
row, form the erect stem. There are from two to five 
branches in each circle, and one or more of them may 
bear one or two smaller branches. On the tip of each 
branchlet there grows a small, oval spore, which falls off 
on being wetted. They suggest for this Fungus the 
name of Verticilliwm atro-album. Mycelium was found 
in the tubers, even on plants that appeared moderately 
healthy. : 
Potato—continued. 
affected in either of the above ways are almost always 
diseased, and produce shoots that, from their first-appear- 
ance, are evidently diseased. These shoots develop slowly, 
and remain small, stunted, and of an unhealthy colour. 
Dark spots appear on the leaves and on the leaf-stalks, 
and the leaves gradually wither from below upwards; 
and similar changes go on in the stems. The plants 
perish without being able to form new tubers. No Fungi 
have been detected in the leaves or stems of shoots 
produced by diseased tubers; but all the subterranean 
parts have the bark permeated by mycelium, though 
there is none visible in the woody bundles. The diseased 
tubers show an abundant mycelium in the corky layers 
of the skin. Cultivation of the mycelium, in each case, 
has yielded FV. atro-album. Inoculation from diseased 
plants rendered previously healthy plants diseased; and 
healthy tubers planted in soil impregnated with conidia 
of V. atro-album produced diseased shoots. Reinke and 
Berthold suggest that V. atro-album may be an imper- 
fectly-developed condition of some Pyrenomycetous 
Fungus of the genus Nectria, or closely allied to it, 
and oppose the view advocated by Hallier, that the 
cause of Potato Curl is Pleospora polytricha; nor do 
they think the disease is caused by any species closely 
allied to the genus Pleospora. Schenck, in a series of 
observations and cultivation of the diseased plants, ob- 
tained from some of them Fungi which were much like 
one form of conidia attributed to Pleospora herbarum, — 
and which he called Sporidesmiwm ewitiosum var. Solani. — 
It is evident that there is need of further observations, 
since there may be more than one cause of this disease, 
and true parasites may be confounded with Fungi that 
grow only on tissues already dead, No cure is known; 
hence, prevention is the aim to be kept in view. Diseased 
plants should be pulled up and removed as soon as de- 
tected; and all the Potato-stalks should be collected into 
heaps and burned. Care should also be taken to prevent 
unsound tubers from being made use of as seed. In 
short, the means employed to limit the spread of Potato 
Rot, and of Peziza postwma, are equally applicable against 
Potato Curl. 
In common with other herbaceous plants, the Potato 
affords, in its dead stems and leaves, an abundant food 
supply to many kinds of Micro-fungi; but, as none of 
these are known to be injurious to the plants during life, 
they do not require even to be enumerated here. — 
Potato tubers are rendered unsightly, at times, by the 
skin being more or less covered with brown patches or © Lees 
scabs. These may be due to various causes. In some | 
cases, a microscopic examination shows that the scab is 
due to the growth of a Fungus, named Tubercinia 
scabies, the spores of which are formed of small cells, 
grouped into a globe around an air space. Each spore 
has a slender stalk at one side. There is often no trace 
of this Fungus at harvest-time; but, during the winter, 
it develops, and the spores form a layer beneath the 
skin, often extending over a great part of the tuber. _ 
After a time, the spores are set free by the bursting of 
the skin. In other forms of scale, the cells are filled 
with mycelium of Fungi, and the formation of the scab 
is probably due to the irritation caused by its presence 
in the tissues. In others, there is no trace of the action 
of Fungi; and it has been conjectured that the cracks, 
followed by scabbing, are due to contact with irritant 
or corrosive substances in the soil, and that the scabs 
are due to efforts at healing the injury; but new cracks 
form in them, and so the mischief goes on. The raw 
| surfaces of the cracks render the tubers more liable to _ 
injury from Fungi, insects, frost, and other external 
causes. Scabbed Potatoes are diminished 
unfitted for food when the skin is 
ai should not, however, be used as seed. When the cause 
i | in valie 
because of their unsightliness; but they do not seem 
