THE NATIONAL NURSERYMAN 
163 
pkytes becoming parasites under other conditions or of host- 
plants changing their susceptibility. He hardly know anything 
of the scientific base of this changing. We do not know whether 
the host plant is changed or the fungus. We only know that 
their relations have a different aspect. 
We accept the possibility that fungi and bacteria, which cause 
severe diseases in the United States, may cause as severe an epi¬ 
demic here. 
I am going to follow the lists of imported plant products into 
Rotterdam harbor, for my conclusions. And I will speak of the 
parasites of plant products for propagation as well as for con¬ 
sumption. 
The importation of fruit is becoming larger and larger. Apples 
were imported into the harbor of Rotterdam: 5000 KG in 1920, 
208,000 KG in 1921; nuts increased from 288,000 in 1920 to 
590,000 in 1921. 
A severe apple disease, the bitterrot, caused by Clomerella cin- 
gulata (Glososporium fructigenum ) exists in America. This kind 
of fungus also lives in Europe, without doing harm, but we also 
know by the researches of Kruger, that in Europe the strain 
(as we call it in mycology) of the fungus is different from the 
American strain, as well in morphology as in virulence. It is 
possible that the virulent strain will be carried from America 
as small spots on the apple, and it may possibly cause epidemics 
here as severe as in the United States. I will also draw your 
attention to a disease of nuts, common in California, the walnut 
blight, caused by Paeuilomonas juglandis. When young the nuts 
are exposed to a severe rot, which if attacked actually kills them. 
But the late infections (after the researches of C. O. Smith and 
H. Ramsay) only give “a very shallow, superficial development of 
the disease.” I am well aware that these nuts—imported are not 
used for propagation, but they may carry the bacteria and this 
case is comparable to the many cases of the American patholo¬ 
gists. 
As to the seeds we know that clover seed has always been 
imported from United States to Western Europe (15,000 KG in 
1920, 11,000 in 1921). In scientific phytopathological publications 
the question of parasite-importation on this seed is often men¬ 
tioned, as we know, that American red clover seed is mixed with 
European in the market. Merchants generally advertise their 
seed as being unmixed with American varieties, as they know 
it often is attacked by Anthracnese ( Clososporium Cauliverum). 
I do not think it was quite proved on a scientific base, though 
it is highly probable that it has been imported. In Germany it 
has been often found on crops from American seeds and the gen¬ 
eral opinion is that American varieties are more susceptible. 
The importation of wheat, mais, rye, barley, oats and buck¬ 
wheat is of the greatest importance, especially as a good stuff. 
Through the latest agricultural quarantines of the United States 
of America we know that the United States is afraid of import¬ 
ing fungus parasites through the grain seeds “imported for con¬ 
sumption.” Quarantine 39 is an example. It demands a certifi¬ 
cate that the seeds imported were grown in a place free from 
Ophiobolus graminis (take-all disease), which they find men¬ 
tioned in Japan, Australia, France, Italy, Germany, Great Britain, 
Ireland, Belgium and Brazil. This take-all disease is caused by 
a parasite, Ophiobolus, which attacks the plant at the stem base 
and which has no flying conidia, which might infect the seed. 
The ascospores of the fungus are liberated during the winter 
or early spring and remain in the soil until the required amount 
of moisture and temperature induces germination. Mangin ob¬ 
served the germtubes enter the wheatplant through the root hairs. 
I do not think it possible that seeds could carry or transmit any 
propagation organs of the fungus. If they were carried it could 
only be by the straw, though it will probably remain in the 
stubble, but certainly not with the seed, even in an uncleaned 
state. 
The Americans say that the disease is not heretofore widely 
prevalent or distributed within and throughout the United States. 
Are the Americans sure it is “prevalent” in the countries men¬ 
tioned above? I know that our knowledge of the Ophiobolus 
disease is very small indeed and that there is more than one 
Ophiobolus disease. The economic importance of the diseases is 
not large; it has been studied insufficiently and the transmission 
of the disease by seed highly improbable. Besides in the United 
States, the disease does occur. In the American phytopathologi¬ 
cal literature of the last years, another disease of grains in the 
United States is mentioned, which unfortunately has the same 
name, take-all, but of which the cause is undetermined. It is 
described in Farmers’ Bulletin 1226, of the U. S. Dept, of Agri¬ 
culture. In 1920 it was found in Illinois. It is supposed that a 
Helminthosporium is connected with it. If Europe is going to be 
afraid of this “unknown” disease, we will probably get into a 
muddle about the name “take-all,” and before we really know 
what it is. As Quarantine 37 was established in 1919 and the 
new “take-all” only appeared in 1920, this name should be abol¬ 
ished by scientists. We cannot make out what the danger is of 
the “Illinois take-all” for Europe. The large shipments of cer¬ 
eals, even when used as a foodstuff only, will probably put Euro¬ 
pean agriculture on a lookout. 
In the year 1920, 124,000 KG of beans were imported into Rot¬ 
terdam harbor alone. In America, beans are severely attacked 
by a dangerous disease, which might be carried to Western 
Europe. It has never been found with scientific certainty on this 
side of the Atlantic yet. The disease of the beans is called the 
bean blight ( Bacterium phaseoli). But America’s famous bac¬ 
teriologist, Erwin Smith, thinks it highly probable that it is 
commonly carried on the seed. The more so as Edgerton’s ex¬ 
periments seem to prove it. Erwin Smith says that it affects the 
seed coat, without destroying the seedling embryo, and the or¬ 
ganism has a great resistance to drought. It is a well-known fact 
that it is a dangerous disease in a moist climate. The bac¬ 
terial spots are seen on the leaves as minute translucent dots 
which become somewhat protuberant, later sunken and discol¬ 
ored. The pods are also heavily infected and finally the ripening 
and the grown out seeds. The United States and South Africa 
are the places where it occurs very often. 
i ^ nc ^^ a * n ’ w ^ a t a bout the vegetable seeds, of which in the 
year 1920 16,000 KG were imported into the port of Rotterdam? 
The pathology of the vegetable seeds is only partly known In 
the case of several diseases, the way in which these diseases 
are transmitted is not known, but there are indications that a 
number of these may be carried by the seeds. 
In the United States there is a dangerous bacterial disease of 
the tomato, caused by Allanobacter michiganonse, which causes a 
paloemdisease. It shows a withering of the stems, a leaf wilt and 
finally a rotting of all the tissues. Erwin Smith says of it, “I 
think that it is a seed-borne infection. I have seen its yellow 
slimes close under the seeds in the middle of green tomato fruits 
and also in the coat of an immature seed.” Whether or not, it 
actually occurs in the interior of seeds, capable of germination, 
the frequent extensive invasion of the outer part of the tomato 
fruit is certain to bring about a surface contamination of the 
seeds. 
These examples illustrate some of the dangers that threaten 
European horticulture and agriculture. If Europe follows the 
same lines, her points are as convincing as the American are. 
England has in 1921 issued an order against four American 
plant diseases, the chestnut canker ( Endothia pavasitica) , downy 
mildew of hops ( Peronoplasmopara humili), pear blight, {.Bacil¬ 
lus umylovcvus) , black knot of plum {Plowvightia viorbosa). 
From a purely scientific standpoint the two fruit diseases may 
be carried over by fresh fruit; the order will also be of value in 
case of blight and black knot, when scions and twigs are sent 
from the U. S. to Europe; so it is with the chestnut canker, 
which is a real twig parasite. The order shows that the inter¬ 
ests of English horticulture and agriculture are focussed on this 
point. 
Before trying to answer the second question (whether the 
danger is so large as the United States makes us believe) I 
want to make some remarks on Quarantine 37. 
Quarantine 37 of the United States has been the focus of 
interest of horticulturists. It has been criticized by different 
scientists, by our phytopathological services a. s. o.: So it nearly 
seems superfluous to speak of it again. 
There are only some questions that arise from a scientific 
standpoint and which I should like to put to you. 
I take as a base that every cultural plant which may not be 
imported is refused on account of a special disease. If now I 
see that the peony and the gladiolus are excluded (the import 
occurs only by special permit), I can only think of two diseases. 
The peony suffers in the United States and in Western Europe 
from Botrytis Pasonias Oud. In the United States it is very 
common and has been studied at different phytopathological 
places. I have the impression that it is more common in the 
United States than it is here, but at both sides it is well known, 
and there is no danger of harming each other, on either side. 
With the gladiolus it is the same thing. The only disease that 
has certain influence is the hardrot that is caused by the fungus 
Bepteria gladioli. This occurs at both sides and was first de¬ 
scribed in the United States by Massey. 
The growers here know it well and in the United States it is 
wide-spread. For a phytopathological scientist it is absolutely 
incomprehensible why these plants are excluded. 
The same may be said of the dahlias, of which as far as I 
know, no dangerous infectious disease exists. 
Let us now have a look at the practical side of the question and 
catch a glimpse into the lists of the fungal and bacterial para¬ 
sites America has found in different shipments of plants from 
Holland. It will show to us whether the shipments of plants are 
loaded with parasites. 
The phytopathological service has already pointed out by 
analyzing these lists how clean the plants are and how few para¬ 
sites are to be found in them. 
