October 2, 1884. ] 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
313 
obtained. The last-named cross has been attempted, but unsuccessfully, 
though if one has failed others might succeed, and a totally distinct race 
would doubtless be produced.— Lewis Castle. 
FUNGI AND DISEASES OF PLANTS. 
By T. J. Burrill, Illinois Industrial University. 
{Continued from page 222.) 
OKIGIN AND DEVELOPIIENT OE FUNGI. 
The idea is too common that such things as mould on moist bread, 
black velvety stains on the surface of Peaches, itc., may spontaneously 
occur through some combination of climatic effects, without the necessity of 
pre-existing germs of each particular kind; but these things no more arise 
in this manner than a young Peach tree starts from a ball of clay peculiarly 
mixed, or from the seed of an Oak. Each fungus produces its own seed-like 
bodies, “ spores,” and from these alone is their reproduction possible. One 
mildew does not change it into another one, and none are anywhere 
developed except as offspring of parents, as among the higher inhabitants 
of earth. Where, therefore, the germs of any particular parasitic fungus do 
not exist, no possible combination of circumstance or of things can cause 
such fungus to spring up into life and development. Were it not for the 
existence of the special kind of spores capable of germination, no amount 
of showery weather would make Wheat rust, nor fog and rain cause Grapes 
and Peaches and Apples to rot. Neither are these spores gifted with any 
powers of distribution beyond that afforded in the regular order of nature. 
They are carried by the wind, but cannot float in still air ; gravitation as 
surely brings them to earth, save when carried by stronger forces, as it 
does cannon balls and meteorites. As we gain knowledge of the facts and 
processes of Nature the powers of good or evil genii of the air diminish, and 
at last their existence is altogether denied. No one of intelligence now 
believes witches by acts of will blast the crops and curse the fields. The 
reign of universal law, affecting alike the minute and the great, the in¬ 
organic and the organic, the dead and the living, the nerveless and the 
sentient, is acknowledged and verified by the science of our day. Things 
do or do not take place, not according to chance or supernatural power, but 
according to the regular and orderly procession of natural law established 
and perpetuated by Him in whom there is no variableness nor shadow of 
turning. Every efect has its cause, and we ought never to think any of 
these causes are past finding out or beyond the comprehension of man. 
With the knowledge we now have concerning all, including the most 
obscm’e and minute species of living things, there can be no hesitation on 
the part of the informed~n accepting the present existence of any fungus 
growth as positive proof of a pre-existence of its special germ, and of the 
development of that germ under sufficiently favourable conditions. Plant 
diseases occur as new in given localities though the soil, climate, and cultiva¬ 
tion of crops are as nearly as possible as they have been for many years. It 
is only recently that one of the mildews on American Grapes appeared in 
Europe, though it is already widely spread on the continent and is the cause 
of much alarm. The conditions of weather and of the Vine have for 
generations been as favourable for the growth of this mildew as they are 
now ; only one element has been wanting—the spores. The latter have 
finally crossed the ocean, in some way carried by man, and now the rapid 
development proves the suitableness of the existing conditions for growth, 
but their inadequacy for original production. In the same way the black rot 
of American Grapes can be traced to infection from Europe, and the same 
lessons arrived at. 
A few years since a parasitic fungus previously known in South America, 
gained introduction to southern Europe and gradually spread over the con¬ 
tinent, carrying destruction to the Hollyhock as it went. Reaching England 
its ravages were especially marked, since considerable prominence is given 
this popular flowering plant. The Hollyhock is closely allied to the Cotton 
plant, and as these fungi sometimes grow on botanically related species there 
was cause for apprehension lest the parasite should be again transported 
across the Atlantic and bring serious trouble to our sisterhood of Southern 
States. The watery bearer was actually passed, but fortunately the Cotton 
did not prove susceptible to its withering effects. 
The primitive origin of these species of fungi we will not discuss. They 
in some way, at some time, came into existence, and in the same manner that 
other species of living beings, not excluding man, were originally produced. 
Evolution has been studied, and in its light species are said to be transforma¬ 
tions of previously existing species ; but this does not in any practical sense 
affect the foregoing, because the process is reckoned by centuries and eons, 
not by years or the generations of men. 
It is possible that change of habit sometimes occurs to such an extent 
that a fungus species not formerly capable of growing on a certain host 
species, becomes adapted to the latter ; but nothing of this kind has been 
definitely observed. There is, however, the widest variation among the 
species of parasitic fungi as to the limits of their restriction to certain host 
plants. Many are found only on one species; very few (except such as have 
a peculiar alternation of habitat after the manner of many animal parasites) 
grow on plants belonging to different botanical families. Yet a few affect 
many species of flowering plants, even sometimes those of quite different 
orders. In the latter cases there is usually more or less difference in the 
vigour and appearance of the fungus on the different hosts ; so that it is not 
easy to decide by form and appearance alone whether a certain parasite on a 
certain nourishing plant is, or is not, a distinct species, or only a modified 
condition of something known elsewhere. Artificial cultures, by transferring 
the spores from plant to plant and w'atching their development, are the only 
criteria when such doubts occur; and this is entirely feasible, though it 
requires much care and skill to secure reliable results. The so-called black 
rot of Grapes is caused by a minute fungus parasite of low and simple 
organisation affecting the young stems and leaves (petioles and veins), as 
well as the fruit. There is also a disease of the canes and leaves (petioles 
and veins) of Black Cap Raspberries and Blackberries caused by a little 
fungus so similar in every way as seen under the microscope that one is 
inclined to pronounce them identical ; but cultures prove them distinct—a 
point of considerable practical importance. 
GERMINATION AND PENETRATION. 
The next thing deemed of most importance is to fuUy comprehend that 
these parasites always germinate outside the plant tissues and gain 
entrance, if at all, only by mechanically penetrating the epidermis, or other 
surface coat. An unsubstantiated opinion too commonly prevails that in 
some way the spores may be taken up by the roots with water and carried 
with the latter to any part of the plant. This assumption is founded upon 
a misconception of the manner that plants take water from the soil, and of 
the way it traverses the plant tissues. It is true there are in most plants 
elongated ducts or tube-hke vessels, the open cavity of which is sometimes 
large enough to be seen in cross section by the unaided eye, and large 
enough to pass many fungus spores; but these cannot, in any just sense,be 
compared to the arteries and veins of animals. The truth is, when there is 
any considerable movement of the watery fluids in plants, these ducts are 
always filled with air, not with liquid material. If a sapling in full leaf, 
and consequently in its most active state as to the ascent of water to supply 
the marvellous amounts transpired, is cut and a portion of the stem thrown 
into water, the latter will be sucked into the tissues to the amount of 10 to 
20 per cent, of the weight of the green stem, clearly showing that the wood 
was not previously full. Other experiments and investigations prove that 
the water normally ascends (and descends sometimes) through the sub¬ 
stance of the cell walls themselves, not through the cell cavities. Now, no 
one is able to see with the best microscope ever made the mter-molecular 
spaces in these cell walls, though water, itself made up of solid molecules, 
passes through them to gain entrance in the first place to the roots, and 
through the millions of them in its progress to the upper portions of the 
plant. No fungus spore can pass such filtering. The methods of freeing 
liquids from solid particles practised by chemists are coarse and sorely in¬ 
adequate compared with that in operation in plants. It is absolutely im¬ 
possible for any solid body large enough to be seen at all by the highest 
microscopic powers in existence to pass through one such cell wall, much 
less through the unnumbered myriads composing the tissues of one of our 
ordinarily cultivated plants. All spores of fungi rarely are less than one 
five-thousandth of an inch in diameter, while a body less than one hundred- 
thousandth of an inch can be seen and studied, and as the molecular 
openings through which water passes are still less, probably much less, we 
may be certain that such spores are effectually excluded from the circula¬ 
tion in the plant tissues. Direct examination also proves that the entrance 
of the fungus is affected by piercing the surface ; the germinal tube accom¬ 
plishing this by its power of absorbing the substance at the point of con¬ 
tact, or by reaching and passing through a stomato. A thick epidermis is 
often a complete safeguard against the former method, this alone being 
sufficient to account for the immunity of certain varieties from disease.s 
which so nearly exterminate others. It is scarcely possible that any para¬ 
sitic fungus should be able to make its way through the corky envelope of 
tree trunks, &c., which we call bark, so long as the latter is free from cracks 
or wounds. 
It must be remembered that to exist a fungus is as dependent upon an 
organised structure as are other plants and animals. It is not possible that 
this solid structure can be dissolved and life continue; it is not possible 
that a fungus spore can bo liquified, absorbed, and reorganised. As well 
might a criminal think of reducing his body by some chemical process to a 
liquid form in order to j)ass through the merciless grating of his cell window, 
and live afterward as a man. 
As a practical demonstration of the non-absorption and non-circulation 
of fungus spores in the tissues of plants, nothing can be more satisfactory 
than the results as known of putting bunches of Grapes in paper bags to 
prevent the rot so prevalent in our country. These diseases, for there are 
several of them, are perfectly prevented by excluding the spores of the fungi 
which produce them from the fruit itself, though the rest of the Vine is not 
protected. As a matter of fact, other parts of the Vine are parasitised by 
the same depredators, and sometimes serious injury done; but the effect is 
necessarily different from what it is in the true pulp of the fruit. In these 
cases, and in most cases, the mycelium, or root-like portion of fungi, spreads 
but slightly from the first point of entrance, not more than a few hundredths 
of an inch in the stems and leaves, to a greater distance in the fruit. But 
a limited number of species uniformly send their mycelium very widely 
through the affected plant. Smut of Wheat shows itself only in the head, 
but the fungus starts in the germinating plantlet and traverses the whole 
length of ti'e straw. 
The conditions of germination are also important elements in a study of 
plant diseases due to fungi. The spores are very simple in structure; each 
consists of a single ceil formed of an enclosed mass of plastic sub¬ 
stance (protoplasm) around which are two coats, the inner thin and 
flexible, the outer usually thicker and much less elastic. In germination 
the outer is pierced or cracked, and the inner coat proti’udes as a long tube 
containing still the soft internal substance. This tube is that which 
penetrates the plant, becoming perhaps a hundred times as long as the 
spore before gaining access to the hypodermal tissues. A proper tempera¬ 
ture, varying with the species, is essential for this process, but still more 
marked are the conditions respecting moisture. A fungus spore can no 
more germinate without water than can a seed of a flowering plant, though 
neithei requires to be immersed in water. Damp air, such especially as we 
have during fogs, favours the germination and penetration of fungi. Some¬ 
times these processes take place on leaves and fruit when more or less 
covered with httle drops of dew. In bagging Grapes, should any of the 
rot-spores be included it is by no means probable that they would germinate 
on account of the want of water, and this is the secret of Grapes so often 
escaping the disease when the Vines are protected by being trained under 
the eaves of a building or similar shelter. This influence of water upon 
germination is one of the important reasons why most parasitic fungi 
make worse depredations during wet than during dry weather. In most 
cases the spores themselves are more readily and widely distributed 
when dry. 
Violas, —These have done so well this year in many places that they 
will no doubt be more cultivated than they have been. In Countess of 
Hopetown we have a great acquisition, for it is a robust-growing sboit- 
jointed variety of close compact habit and a thoroughly good bloomei; 
not so pure a white as Mrs. Gray, but then it never flushes in colour as 
Mrs. Gray sometimes does. It is a very fine bedder, Mrs. Gray is still 
