500 
in establishing the isostatic theory on a firm basis. 
This point, for which there is no direct evidence in 
the Norwegian case, is to the effect that the tilting of 
the Great Lakes region was in progress before and 
during the rise of the sea in the Ottawa valley, for, 
presumably from a comparison of contemporaneous 
ice-margins, it is concluded that “the Ottawa valley 
must have been, in part at least, occupied by the ice- 
sheet during the existence of Lakes Iroquois and 
Algonquin, and at least a small amount of uplift 
affected the region at the foot of Lake Ontario during 
the life of Lake Iroquois. Uplift also affected the 
northern portion of the Great Lakes region, and 
probably included the upper portion of the Ottawa 
valley near Mattawa during the existence of Lake 
Algonquin, and while the ice-sheet still occupied the 
upper portion of the Ottawa valley.” Further, it is 
not a case of alternating elevation and depression, 
“for the result of investigations by numerous geo- 
logists of the raised beaches of the Great Lakes 
region has shown that differential uplift took place 
almost continuously as the ice withdrew.” 
We have thus direct proof that a district which was 
rising relatively to those around it was nevertheless 
vundergoing submergence beneath the level of the sea. 
‘This remarkable phenomenon can have but one ex- 
planation, namely, that the isostatic recovery and the 
general rise of the ocean-level were in progress simul- 
‘taneously, and that for a time the latter was the more 
rapid. Norway up to the present has only supplied 
a measure of the difference of these two motions. 
To presume their concerted action was a leap in the 
dark. Canada has now produced unexpected evidence 
of their individual existence. 
There is now but one thing wanting to make the 
analogy between the isostatic phenomena of America 
and Europe perfect in every detail, and that is the 
discovery of a shore-line corresponding to the ‘‘ Early 
Neolithic’? or ‘‘Littorina-Tapes’’ raised beaches of 
Great Britain and Scandinavia. This should represent 
in the south a distinct resubmergence, and in the 
north a pronounced check or slowing down in the 
‘general emergence. W. B. Wricut. 
PLANT DISEASES. 
"TRE réle played’ by insects in the spread of plant 
diseases is well brought out in the case of the 
collar-rot of rubber trees (Hevea brasiliensis), recently 
investigated by Sharples (Bull. 25, Dept. of Agricul- 
ture, Federated Malay States, 1916). The disease is 
caused by the fungus Ustulina zonata, as Brooks 
(Bull. 22, F.M.S.) has already shown. Sharples finds 
that at the time when the trees in a young rubber 
plantation are thinned out, at the age of about six or 
seven years, attacks by boring beetles (Xyleborus par- 
vulus) become very common. He shows that these 
insects: easily enter trees the bark of which has been 
injured by the falling of one tree against another. 
Attacks by the above-mentioned fungus usually quickly 
follow the beetles which enter rubber trees, the tracks 
of the insects being convenient ports of entry for the 
wound-parasite, U. sonata. At the time of thinning 
a large amount of suitable food material for the fungus 
is available in the form of soft rubber wood. Owing 
to the increased development of the fungus under these 
conditions in conjunction with the greater prevalence 
of borer attacks during the same period, it follows 
that the thinning-out stage is the most dangerous one 
‘in the life of a plantation as regards the attacks of this 
fungus on rubber trees. 
To No. to of the twelfth volume of the South African 
Journal of Science, published in May of the present 
year, Dr. Ethel M. Do‘dge contributes a paper on 
ithe occurrence in South Africa of Bacterium campestre, 
NO. 2469, VoL. 98] 
NATURE 
[FEBRUARY 22, 1917 
the organism which causes the black-rot disease of the 
cabbage and other cruciferous crops. This organism 
had formerly been recorded only from Europe, America, 
and New Zealand, but Miss Doidge’s investigations 
showed that the disease caused by it was quite common 
in the neighbourhood of Pretoria. The most interest- 
ing point about the communication is that it seems 
| clear that the organism in the case under considera- 
tion was introduced into South Africa on cabbage seed 
which came from England. From cabbage seeds im- 
ported by the nuseryman to whose premises the dis- 
eased plants first observed by Miss Doidge were traced, 
the organism was isolated and its virulence proved by 
the successful artificial inoculation of two healthy 
cabbage plants. It was suggested nearly twenty years 
ago by Stewart in America that this. disease was 
probably disseminated by seedsmen, but actual proof 
was then wanting. Soon after this the organism 
was isolated by Harding from the surface of cabbage 
seed produced by diseased plants in Long Island; and 
now Miss Doidge has shown that by such means the 
disease may be carried from one continent to another. 
Soaking suspected seed for fifteen minutes in 1: 240 
formalin or in 1: 1000 mercuric chloride is recom- 
mended as a suitable method of treatment. 
The cause of the serious disease of the potato known 
as the ‘*‘ Blattrollkrankheit ’’ (leaf-roll disease) has been 
a matter of considerable controversy. The earlier 
investigators regarded the disease as being due to the 
choking of the wood-vessels of the plant with fungus 
mycelium. Recent researches, however, have shown 
that plants suffering from the choking of their vessels 
(hadromycosis) are not to be confounded with those 
affected with the true leaf-roll disease in which 
mycelium is absent. Quanjer, in 1913, found necrosis 
of the phloem to bea characteristic symptom of true leaf- 
roll in Holland ; and in his most recent publication (Med. 
van d. Rijks Hoogere Land-, Tuin- en Boschbouw- 
school, Deel x., Wageningen, 1916) this author claims 
to have proved that the disease is due to a transmissible 
virus. Since attempts made to infect healthy potato 
plants by means of injections of the sap of diseased 
plants did not succeed, it might be thought that the 
claim is not justified. However, successful trans- 
mission of the disease was brought about in grafting 
experiments both with stalks and with tubers. Further 
evidence in favour of the virus is claimed to be afforded 
by the failure to isolate any parasitic organisms from 
affected plants, by the method of spread of the disease, 
by the uncertain results of selection as a means of 
raising healthy stocks of plants, and by the infection 
of healthy plants when transferred to diseased sur- 
roundings either through the agency of the soil (in 
which it is believed that the virus is often present) or 
from neighbouring diseased plants. It would seeul that 
further research is necessary in order to supply abso- 
lutely convincing proof of the virus theory of the 
origin of this disease. Should it turn out to be a 
correct one, this disease, which has already made its 
appearance in some parts of Great Britain, will prob- 
ably become more or less widespread in a few years 
unless some measures are taken to check it. The 
publication referred to is published in both the Dutch 
and the English languages. 
COAL AND ITS ECONOMIC UTILISATION.* 
HE economic importance of coal we perhaps 
realise. It is the only raw material we produce in 
great quantity; the value of our total mineral output 
in 1913 was above 160,000,000l.; of this the value of 
the coal at the mine was above -145,500,000l. j 
Our output of coal and our home consumption- in | 
1 Abridged from the Howard Lectures delivered before the Royal Society 
ieee on November 27, December 4, and December rr, 1916, by Prof 
db. S. Mrame. - 
