372 
THE TROPICAL AGRICULTURIST. [Dec. I, 1903. 
methods are applied foe deriving them from the vast 
stores which are always in reach with the tide of 
suitable appliances. 
GREEN CROPS IN MANURE. 
The growing of green crops for manure benefits the 
land not only by returning to the soil that which may 
have been derived therefrom and from the air, but also, 
through the chemical action of plant roots, which 
have the capacity of changing the characteristics of 
the various "salts" in the soil, and as the roots of plants 
appropriate carbonic acid as an agent in neutralizing 
the alkaline matter, various compounds are formed. 
Alkalies also neutralize acids, and there is a constant 
tendency to effect chemical changes by reason of the 
use of green foods, manures, fertilizers, plaster or lime. 
The soil is the bank of the farmer upon which he can 
draw, but he must first make his deposits. Cultivation, 
tile drainage, the use of certain crops and a knowledge 
of the characteristics and requirements of the soil will 
give the intelligent farmer a great advantage over him 
who does not carefully consider the reserve of plant 
foods in the soil. 
' » 
THE CANKER FUNGUS IN RUBBER. 
Mb, J. B. CAERUTHERS ON THE DISEASE. 
A special general meeting of the Kalutara Planters' 
Association was held at the Tebuwana resthouse on 
Saturday afternoon, October Slst, to hear Mr. J. B 
Carruthers, Government Mycologist, on the question 
of Canker in Rubber, which has made its appearance 
in the Kalutara district. 
MR. CAREUTHEES' ADDRESS. 
Mr. J. B. Carruthers, who, on rising was received 
with applause, said : Gentlemen, to begin with the 
history of the disease, I may mention that it was 
first noticed two years ago by the Assistant Conser- 
vator of Forests of the Province of Sabaragamuwa ; 
but it was not till some five months ago that my 
attention was called to it. Following this various 
diseased specimens of rubber were sent to me from 
a number of districts, and, in some of these specimens, 
1 found the neotria or canker fungus. The specimens 
sent contained mycelium, and, on investigating this 
by means of cultures, I found spores, which, on scrutiny 
showed that they belonged to a species of nectria. 
I then made inoculations on trees, and that is the 
only way to prove the guilt of an individual parasitic 
fungus as the cause of any disease. Nectria grow 
on apple trees, plum, cacao, tea, etc., etc., and affect 
and eventually fill many kinds of trees. After these 
preliminary investigations had been to some extent 
finished in the laboratory at Peradeniya, I visited 
Ealntara and went over some fifteen or more estates 
and have seen practically all the rubber estates of 
any size. The result of this inspection is that the 
estimated proportion of diseased trees in the Kalutara 
district is about one in two-hundred or half per cent. 
Yatiporua and Edengoda estates on the oiher side 
of the river are not included in this record. If they 
are included it would about double the percentage and 
make it over one per cent. Yatiporua has about 40 per 
cent, trees afiected by canker and Edengoda 20 per 
cent. The canker has been there for some years, 
possibly five or even more. Details of the effects 
and structure of the fungus will be given in a circular 
of the Royal Botanic Gardens, bo that there is no 
need for me to take up your time with these. Coming 
now to observe the aspect of the disease on trees, 
as a general rule the external appearances on the 
rubber tree are roughened and swollen places in the 
stem and branches. These, on cutting off the outer 
bark, show discoloured tissue, at first a neutral tint 
colour, and afterwards brownish and claret colour. 
When shaved the whole of the diseased parts are 
shown up like an outlined coloured map in the 
lighter-oolonred healthy tissue. When the canker 
fungus has been Krowing in such a spot for some 
time — I cannot definitely say how long, as this depends 
on physiological conditions— the fruits are produced 
at Jfirst pink |or whitish spores, and later round red 
fruits like cayenne pepper, which look, on examination 
under a magnifying lens like crystallized strawberries. 
The structure of these red fruits is the means of 
identifying the fungus as a nectria. The canker 
spreads through the agency of the wind in dry weather 
by water, and by insects such as red ants which 
carry the spores on their legs and bodies in their 
travels over the trees. The only conditions necessary 
for spores to grow are damp and moisture, both of 
which Kalutara always has. As regards the general 
health of rubber in the district it is good, very good, 
notwithstanding the dropping of leaves, drying back 
of young branches and irregular deciduity in certain 
rubber trees. The preventive methods I wonld re- 
commend are inspection by gangs of coolies, cutting 
out the canker and the entire excision of affected 
portions, and the burning of all bark cut off and 
dead branches. The burning of dead branches is a 
most important matter. Personally speaking I believe 
—though I am perhaps rather rash to speak on this 
matter to planters who have practical experience of 
these things— the best way to tackle a disease like 
this is not only to look out for this nectria canker 
disease, but to observe any and all diseases that 
may arise. With regard to the cultivation of rubber 
—as also in the case of other products— a regular 
inspection should be made during a considerable time 
of the year, so that the moment anything unusual 
is noticed in the way of disease it can be treated 
by simple means at the initial stage. As regards 
the time of the year for observing the disease I think 
dry weather is the best. You can see it better and 
also observe the effect of the aaue. The disease is 
better seen in dry weather; it is much more easy 
to spot then than in wet weather. If yon cut out 
a portion of your tree when the weather is damp 
and moist and leave a small portion of the disease 
in the area cut out the fungu.s will struggle on and 
regain a foothold, but if you did that in dry weather 
it would completely dry out the fungus. So that 
there are two reasons to show that dry weather is 
the best for observing and for dealiug with the disease. 
With regard to the applying of mixtures on diseased 
parts, there is no doubt th!>t theoretically and practi- 
cally it is sound, but I have reasons for not 
recommending this. In my experience the farmers 
in England and planters out here very often, if any 
wash is recommended, show a tendency not to carefully 
out out any portion of the diseased bark, but to 
simply smear the bark with the mixture in a general 
sort of way, and the natural result is that the fungus 
goes on in its fell work under the wash, so that the 
treatment is of no avail. If yon cut out the diseased 
portion of the bark and smear the wound with blue 
stone, the result would be advantageous, that is, it 
there is no slovenly work done with regard to rubber 
disease — as in the case of cacao cultivation— the 
Tami) cooly can be shown in a very short space 
of time how to spot the diseased trees. When it 
comes to cutting off portions of the bark in the trunk 
or branches there should be no hesitation. The whole 
of the affected portion is full of the mycelium of 
the fungus and will not produce latex, so that you 
are not damaging your tree to any extent by cutting 
off such portion as is affected. After operation on 
the affected portion the tree will go on' as usual. 
The rubber tree, gentlemen, has a wonderful power 
of growing and producing new tissues. Too much 
importance cannot be attached to this gang inspection. 
Whenever the barK of the tree is rough, and has a 
larger coikey layer than the average bark 1 find 
that where you scrape the bark there is no disadvan- 
tflge to the living tissues of the tree, and it seems 
probable that they are even stimulated by this 
treatment and the amount of latex increased. With 
regard to the production of an abnormal or corkey 
bark it would be well to groom it and see whether 
there is any unhealthy tissue right behind. There 
is one thing that I ought to have touched on, viz., 
with regard to the scare raised by people which 
