646 
Stqjplemeni io ilw "Tropical Agriculturist" [March 1, 19C4. 
mniiy year?. At the pame time it lias been known, 
as a matter of experience among farmer?, t'.iat when 
land is worn out by overcropping, with wheat or 
oatp, for instance, both of which draw heavily on 
the earth's nitrogen supply, certain other crops 
•will still grow luxuriantly upon it, and that if 
these crops are left and ploughed in, the fertility 
of the soil will be restored, and it will again 
produce large fields of wheat and other nitrogen- 
demanding plants. These restorative crops are 
clover, lupin, and other leguminous plants — a 
classification including beans and peas. Everyone 
who is at all familiar with farming operations has 
beard of seeding down an old field to clover, 
thereby restoring its fertility in a degree. 
The great importance of this bit of the wisdom 
of experience was not appreciated by science for 
many years. Then several German experimenters 
began to ask why clover and lupin and beans 
should flourish on worn-out land when otl.er crops 
failed. All of these plants are especially rich in 
nitrogen, and yet they grow well on soil which 
has been robbed of its nitrogen ? Why was this so ? 
It was a hard problem to solve. Botanists had 
already discovered that the roots of the leguminous 
plants — that is clover, lupins, beans, peas, and 
80 on — were usually covered with small round 
swellings, or tumors, to wbicli were given the name 
nodules. The exact purpose of these swelling 
being unknown, they were set down as a condition, 
possibly, of disease, and no further attention was 
paid to them, until Professor Ilellriegel of Burn- 
burg, in Anhalt, took up the work. After much 
experimenting, he made the important discovery 
that lupins which had nodules would grow in soil 
devoid of nitrogen, and that lupins which had no 
nodules would not grow in the some soil. It was 
plain, therefore, that the nodules must play an 
important though mysterious part in enabling the 
plant to utilise the free nitrogen of the air. That 
was early in the 80's. His discovery at once 
started other investigators to work, and it was 
not long before the announcement came. — and it 
come, curiously enough, at a time when Dr. Koch 
was making his greatest contributions to the 
world's knowledge of the germ theory of disease — 
that these nodules were the result of minute 
bacteria found in the soil. Professor Beyerinck 
of Munster gave the bacteria the name Kadiocola. 
{To be continued.) 
TREATME.NT OF TOl^ATO AND CUCUMBER 
DISEASE. 
One of the most disappointing? experiences in 
vegetable gardens is the loss of the tomato crop 
through the fungoid disease which so cotn- 
Ibonly attacks the plant particularly in the low 
country, In our experience the best titUe for 
growing tomatoes in Colombo is between the 
months of October and March. We have also 
found that the plants suffer when exposed oluch to 
tlie sun heat but thrive under partial shade. We 
liave for a long time used and ad Vised the use of 
Bordeaux solution for tomato disease aS the best 
remedy for the trouble, and we have not been 
content with merely spraying but have freely 
watered the plants suffering materially with the 
solution. Furthermore we have also adopted the 
plan of pickling the seed in biuestone solution. 
The treatment advised by Mr. (leorge Massee, of 
Kew, though not from tliat adopted by us, is 
perhaps more simple, and, in view of the success- 
ful results which have attended it, we repro- 
duce the account of the method from the 
Journal of the Eoyal Horticultuial Society for 
October last : — 
In the case of plants growing under glass, the 
conditions are always highly favourable for the 
production of " soft " foliage ; hence their extreme 
susceptibility to infection from fungus spores ; 
whereas plants of the same kind grown out of 
doors or even under glass under more normal 
conditions remain free from disease. 
Under the exceptional conditions of cultiva- 
tion described above, not only do the w'ell-known 
parasites of the tomato ( Cladosponum fulvum, 
Cooke, and Fmarium lycopersici, S icc.) and cf 
the cucumber (Cercospora melonis, Cooke) flourish 
luxuriantly, but certain other fungi, normally 
occurring only on decaying vegetable substances 
in the open, now and again assume a parasitic 
existence when accidently introduced into houses 
where the conditions are so favourable to their 
development; 
The case of Dendryphium comosum, Walk,, may 
be given as an illustration. This minute fungus 
is not uncommon in Britain and other countries. 
It grows on decaj'ing plants, which it frequently 
covers with a dense, dull, olive-coloured mould. 
During the present season, a market gardener 
brought a number of diseased cucumber plants to 
Kew for examination. . . . Microscopic ex- 
amination and repeated cultures and inoculation 
showed the blotches on the leaves to be caused by 
Dendryphium comosum. Further investigation 
showed the fragments of manure projecting from 
the soil in which the plants were growing to be 
covered with a copious developmenc of Z)ertc?ry- 
^AiM/w, and the fungus was fiudlly tmced to the 
manure heap. 
Previous to the present record, Dendryphiutn 
has never been known to act as a destructive 
parasite ; and its becoming so in the present in- 
stance is entirely due to its accidental introduction, 
along with the manure, to a set of conditions wiiich 
enabled it to assume a parasitic existence on plants 
predisposed to disease. Experiments conducted at 
Kew prove conclusively that Dendryphium cannot 
attack cucumber plants growing iu a cool fr.ime. 
The use of fungicides in the form of sprays has 
not by any means produced the results desired and 
anticipated, and experiments extended have demon- 
strated that, under the conditions necessary for the 
rapid production of cucumbers, the daily syring* 
ing and constantly damp surface of the foliage 
render useless those fungicides which, wheu 
applied Under more favourable conditions, have 
proved effective. 
Under the Circumstances, a series of experimeUts 
has been carried Out with the object of ascertain' 
ing whether some substance taken up by the roots 
of cucumbers and tomatoes would not render plants 
thus treated immune against the attacks of fuagug 
