RUBBER AND RUBBER
PLANTING

CAMBRIDGE UNIVERSITY PRESS

HotttJOtt: FETTER LANE, E.G.

C. F. CLAY, MANAGER

too, PRINCES STREET

ILantJon: WILLIAM WESLEY & SON, 28, ESSEX STREET, STRAND

Berlin: A. ASHER AND CO.

1Lfip?tg: F. A. BROCKHAUS

£etoJ Sarfc: G. P. PUTNAM'S SONS

Uombag ant) Calcutta: MACMILLAN AND CO., LTD.

All rights reserved

RUBBER AND RUBBER
PLANTING

y. BY

R. H. LOCK, Sc.D.

Inspector H.M. Board of Agriculture and Fisheries

Sometime Scholar and Fellow of Gonville and Caius College

Cambridge and Assistant Director of Botanic

Gardens, Ceylon

Cambridge :

at the University Press

19*3

Cambridge :

PRINTED BY JOHN CLAY, M.A.
AT THE UNIVERSITY PRESS

PREFACE

DURING recent years interest in the Rubber-
planting industry has extended far beyond that
comparatively large section of the community, which
is engaged in trades more or less directly connected
with rubber. In fact nowadays this material enters so
intimately into the daily life of almost everyone, that
there will probably be few to whom the romance of
rubber entirely fails to make an appeal. In endeavour-
ing to make this book suitable for the needs of as
wide a circle of readers as possible, it has been the
aim of the author to combine an accurate account of
the scientific side of rubber planting with a certain
amount of practical information which may be of use to
the prospective planter. The space available in a book
of this kind only admits of treating the subject in the
form of an introductory outline, but it is hoped that
the information given will be found reliable as far as it
goes.

The science and practice of rubber planting are alike
in their infancy, and in the immediate future important

531

vi PREFACE

developments are to be anticipated both in our scientific
knowledge of the physiological processes underlying the
formation of latex, and in the practical methods of
exploiting this most valuable of raw materials. It is
partly owing to our want of knowledge that it is still
possible to compress into a comparatively small compass
a summary of what is accurately known of both branches
of the subject.

The chapters on the physiology of latex are largely
the outcome of original observations by the writer,
whilst those on planting, harvesting and factory work
on the estate are based on a close personal acquaintance
with the industry in Ceylon. The chapter on disease,
on the other hand, so far as it relates to the fungus
pests of rubber, is little more than a summary of the
work of Mr T. Fetch, whose book is indispensable to
anyone specially interested in this branch of the subject.
I am also indebted to Mr Fetch for the loan of the
illustration of canker on Hevea. Free use has also
been made of Mr Herbert Wright's well-known book
on Para Rubber, and the student who wishes to enter
further into the statistics of rubber cultivation will find
therein a large mass of useful information.

Sir Daniel Morris's Cantor Lectures, delivered in 1898,
still contain the best and fullest account of the wild
sources of rubber, and I have drawn freely upon them
for the information given in Chapter n.

PREFACE vii

The chemistry of rubber has been dealt with only
in the barest outline, but the book seemed incomplete
without some reference to this side of the subject. It is
hoped that the brief summary of the processes employed
in the manufacture of rubber goods will be of some
interest both to the planter and to the general public.
Of both these branches an excellent account on a much
fuller scale is readily accessible in Dr Schidrowitz's book
on Rubber. Other sources of information are acknow-
ledged in a separate list of references.

I am indebted to several friends for advice and
criticism. Mr W. N. Tisdall very kindly read through
the whole of Chapters V, VI and VII, and made a
large number of valuable suggestions, practically all
of which have been incorporated. Mr Tisdall also
provided the estimate given on p. 127. Professor
T. B. Wood was also kind enough to read part of
the proofs.

The text illustrations of different rubber-producing
species have been drawn for me by Mr L. Denton Sayers
— mostly from living specimens — and I am much in-
debted to him for the trouble he has taken with them.
I have also to thank Mr H. F. Macmillan and Mr C.
Northway for the loan of valuable photographs, Mr
Staines Manders for the loan of blocks from the
Catalogue of the New York Rubber Exhibition, and
Messrs F. Shaw and Co. for illustrations of machinery.

viii PREFACE

I should not forget to mention the name of Mr C. O.
Macadam my collaborator in the preparation of the
Ceylon Handbook for the Rubber Exhibitions of 1911
and 1912, since this handbook is in a sense the nucleus
from which the present volume has been evolved.

Finally it is a pleasure to acknowledge that any
literary merit which this volume may possess is largely
due to the untiring help and criticism of my wife, who
has also devoted great care to the preparation of the
index.

R. H. L.

i August 1913.

TABLE OF CONTENTS

CHAPTER I

THE HISTORY OF THE USE AND CULTIVATION
OF RUBBER

Early uses. Vulcanised rubber. The discovery of rubber in America.
The trade in wild rubber. Sir Clements Markham proposes plantations.
Collection of seeds by Collins, Wickham and Cross. Hevea brasiliensis in
Ceylon. Early experiments. Rise of the plantation industry in the East.
Area under plantations. Production from estates. Variations in the price
of raw rubber. Capital involved pages I — 15

CHAPTER II

THE BOTANICAL SOURCES OF RUBBER

List of species. American species. Hevea brasiliensis. Economic
aspects of the Amazon rubber industry. Manihot species. Castilloa.
Hancomia and other species. Guayule rubber. African rubbers.
Funtumia. Landolphia. Other African species. Asiatic rubbers.
Ficus clastica. Jelutong rubber 16 — 37

CHAPTER III

THE PHYSIOLOGY OF LATEX PRODUCTION

The structure and functions of the vegetative organs. The laticiferous
system. Latex tubes. Latex vessels. Structure of the bark of Hevea.
Minute anatomy. The effects of wounding the bark. Renewal of bark.
The functions of latex. The composition of Hevea latex. Coagulation.

38-55

TABLE OF CONTENTS

CHAPTER IV

THE PHYSIOLOGY OF LATEX (continued)—
TAPPING EXPERIMENTS

Method of experiment. Wound response. Reasons for the increase of
yield. Duration of yield. Relation of yield to volume of bark. Origin of
latex. Seasonal variation. Effect of climatic conditions. Variation in
yield of individual trees. Tapping intervals. Overlapping. Yield at
different levels of the trunk. Effect of tapping on the composition of the
latex. General remarks on yield. Resting periods. Effect of tapping on
the tree. Summary 56 — 92

CHAPTER V

HEVEA. PLANTING OPERATIONS

Choice of situation and soil. Clearing. Nurseries. Seed selection.
Draining, irrigation, roads, etc. Lining and spacing. Holing and planting.
Rate of growth. Weeding. Intercrops. Cultivation and manuring.
Green manuring. Shade and wind belts. Pruning. Thinning out.
Labour. Other expenses. Tools 93 — 127

CHAPTER VI

HARVESTING OPERATIONS

Incision methods of tapping. Methods in use. Excision methods.
Systems of paring. Marking the tree. Tapping. Angle of cut. Direc-
tion of cut. Distance between successive cuts. Yields at different levels.
Tapping tools. Plantation yields 128 — 152

CHAPTER VII

FACTORY WORK ON THE ESTATE

The factory. Transport of latex. Coagulation. Washing. Drying.
Creping. Smoking. Smoke curing of latex. Blocking. Scrap. Packing.
The best form of plantation rubber. Sales and markets. Quality. Defects
and blemishes. Tackiness 153 — 175

TABLE OF CONTENTS xi

CHAPTER VIII

THE PESTS AND DISEASES OF HEVEA

Plantation conditions. Epidemics. Wind. Animals. Insects. Termes
Gestroi. Fungus diseases. Diseases of the roots. Fames semitostus.
Brown root disease. Diseases of the stem. Canker. Pink disease.
Die-back. Burrs and nodules. General sanitation . . 176 — 196

CHAPTER IX

THE CULTIVATION OF SPECIES OTHER THAN HEVEA
BRASILIENSIS

Castilloa. Manihot. Funtumia. Fitus elastiea . . 197 — 209

CHAPTER X

THE CHEMISTRY OF INDIA-RUBBER

Difficulties of study. Composition of technically pure rubber. Physical
properties. Destructive distillation. Synthesis. Chemical constitution.
Vulcanisation 210 — 219

CHAPTER XI

THE MANUFACTURE OF RUBBER GOODS

Summary. Washing. Drying. Mixing. Preparation of sheet rubber.
Calendering. Miscellaneous articles. Rubber solution. Vulcanisation.
Hot curing. Dry process. Bath process. Cold curing. Reclaimed rubber.
Vulcanite. The testing of rubber goods .... 220 — 237

INDEX 238—245

SHORT LIST OF REFERENCES

1. CLAYTON BEADLE and H. P. STEVENS. Rubber.

2. Catalogue of the Second International Rubber and Allied Trades

Exhibition. London, 1911.

3. Catalogue of the Third International Rubber and Allied Trades

Exhibition. New York, 1912.

4. C. CHRISTY. The African Rubber Industry and Funtumia elastica.

1911.

5. Circulars and Agricultural Journal of the Royal Botanic Gardens,

Ceylon. 1898-1912.

6. J. COLLINS. On the Commercial kinds of Indiarubber. Journal of

Botany. 1868.

7. British Manufacturing Industries, Guttapercha and India-
rubber. 1876.

8. Encyclopaedia Britannica, ninth edition, Article on Indiarubber.

9. Sir CLEMENTS MARKHAM. The Cultivation of Caoutchouc-yielding

Plants in British India. Journal of the Society of Arts. 1876.

10. Sir DANIEL MORRIS. Sources of Commercial India-rubber, Cantor

Lectures. Journal of the Society of Arts. 1898.

11. T. PETCH. The Physiology and Diseases of Heveabrasiliensis. 1911.

12. PHILIP SCHIDROWITZ. Rubber. 1911.

13. CARL OTTO WEBER. The Chemistry of India Rubber. 1902.

14. J. C. WILLIS. Agriculture in the Tropics. 1909.

15. HERBERT WRIGHT. Hevea brasiliensis or Para Rubber, fourth

edition, 1912.

1 6. The Tropical Agriculturist to 1912.

LIST OF ILLUSTRATIONS

PLATE To face page

I. Fruits and Seeds of Rubber Plants . . . 17

II. Tapping wild Hevea 20

III. Forest scene, showing preparation of Hard Para

rubber 22

IV. Anatomy of Hevea 46

V. Hevea Rubber on Swampy Land .... 95

VI. Hevea Rubber and Tea 114

VII. Hevea Tree pricked with Serrated Knife . . 133

VIII. Vacuum Drying Machine 163

IX. Canker of Hevea bark 188

X. Nodules in Hevea bark 193

FIG. PAGE

i. Hevea brasiliensis 18

i. Manihot Glaziovii 24

3. Castilloa elastica 27

4. Funtumia elastica 31

5. Landolphia Kirkii 32

6. Ficus elastica ........ 34

7. Transverse section of Hevea bark ... 46
8, 9, 10, n. Anatomy of Hevea .... Plate IV

12. Tapping areas 58

13. Lining at right angles to a given base . . 106

14. Square and hexagonal systems of planting . . 109

15. Tapping system — full herring-bone . . . 138

16- „ „ half „ „ . . .

17- i) „ half spiral .... „

18. „ „ full „ ,

19- » » Basal V „

20. Method of marking a tree for tapping . . 141

21. Tapping tools — gouge and farrier's knife . . 144

22. Hand Washing Machine 161

CHAPTER I

THE HISTORY OF THE USE AND CULTIVATION OF

RUBBER

Early Uses.

PROBABLY no raw material of vegetable origin has
been put to such multifarious uses as indiarubber. No
other vegetable product has risen with equal rapidity
from a position of comparative insignificance to one of
the highest commercial prominence.

Although the use of rubber by natives of the Western
Hemisphere is historically chronicled upwards of 400
years ago, indiarubber was first used in England in the
eighteenth century, and then only in the first instance
for removing the marks of black lead pencils. The first
patent for the employment of rubber for waterproofing
purposes was not taken out until 1791. The further
development of this use is closely associated with the
name of Thomas Hancock, of the firm of Charles
Macintosh and Co. ; but the modern extensions of
indiarubber manufacture only became possible after the
discovery by Nelson Goodyear in 1839 of the process
of combining rubber with sulphur, which is known as
vulcanisation. Goodyear took out a further patent in

L. T

2 RUBBER AND

1851 for the manufacture of vulcanite by more complete
combination of rubber with sulphur.

Vulcanised Rubber.

The method of vulcanisation, which ranks among
the most important of all industrial discoveries, was
first found out in America by Goodyear. In England,
Hancock shortly afterwards arrived at the same method
independently. The following facts will help the reader
to realise the far-reaching importance of vulcanisation.

Raw rubber becomes soft and sticky when heated,
and when cooled beyond a certain point it becomes stiff
and almost horny in consistency. Vulcanised rubber
retains its physical properties almost unaltered over a
range of temperatures extending from the freezing point
to the boiling point of water. After prolonged immer-
sion in water, raw rubber absorbs as much as 25 per cent,
of its own weight of moisture. On the other hand, "The
water absorption of vulcanised rubber is extremely small
— certainly not large enough to appreciably affect the
insulation of a rubber cable after five years' continuous
immersion" (Weber). From these facts the enormous
increase in the durability and general usefulness of
vulcanised rubber at once becomes apparent. Moreover,
according to the proportion of sulphur which has entered
into combination with the rubber, the physical properties
of the finished product can be made to vary from those
of the softest elastic up to those of the hardest vulcanite.

RUBBER PLANTING

The Discovery of Rubber in America.

As the reader may perhaps have already anticipated,
the first notice of the use of rubber comes to us in the
history of the voyages of Columbus. Columbus found
that the natives of Hayti possessed among other amuse-
ments a game of ball. " The balls were of the gum of
a tree, and although large, were lighter and bounced
better than the wind balls of Castile."

A fuller account was given by Juan de Torquemada
in 1615. This writer describes a tree, called by the
natives Ulequahuitl (Castilloa elastica), which was held
in high estimation in Central America. The method of
collection of the rubber, which flows out as a milky
white substance when the tree is wounded, is described,
and also its coagulation by setting in calabashes and
subsequent boiling in water. Sometimes the latex was
simply smeared over the bodies of the collectors and
allowed to dry — a method still employed by some
primitive tribes. The rubber so prepared was used for
making balls, and for shoes for tumblers and jesters,
whose antics it assisted ; and a medicinal oil was
extracted from it. Even at this early date the Spaniards
themselves employed the milk for waterproofing their
cloaks.

The first accurate account of Para rubber is given by
C. M. de la Condamine, who visited the Amazon country
on an astronomical mission in 1735. He describes

i — 2

4 RUBBER AND

various uses of rubber by the Omaquas Indians, including
that of making syringes or squirts. These instruments
appear to have played an important part in social gather-
ings and even in religious festivals. From this use comes
the Portuguese name Pao di Xirringa, the syringe tree.
Hence also are derived the familiar terms Seringa for
rubber and Seringueiros for the labourers employed in
the collection of this material.

The Trade in Wild Rubber.

The recent development of the trade in wild rubber
may be traced in the following table, which shows the
history for nearly a century of the most important kind,
namely Para rubber, the produce of Hevea brasiliensis.
Prior to the development of the planting industry in the
East, the export of Para rubber from Brazil represented
about half the world's total supply of the raw material.

TABLE I
Exports of Para Rubber from Brazil.

Year Tons Year Tons

1827 31 1870 6,601

1830 156 1880 8,679

1840 388 1890 15,354

1850 1,466 1901 28,161

1860 2,671 1910 38,200

Wild rubbers from Africa and Asia did not begin to
come into the market in large quantities until after the

RUBBER PLANTING 5

Brazilian trade was well established. For example the
exports from the Congo State rose from 30 tons in 1887
to 2000 tons in 1897. At the same date similar amounts
were being exported from Lagos and from the Gold
Coast. A thousand tons of rubber were however
exported from British India as early as 1873.

Sir Clements Markham proposes Plantations.

Herbert Wright has called attention to the fact
that it was Hancock who in 1834 first suggested the
possibility of cultivating the best kinds of rubber trees
in the East and West Indies. The suggestion arose on
account of the difficulties which Hancock and his
colleagues experienced even at that date in procuring
a sufficient supply of raw material. The actual birth
of the rubber planting industry, however, dates only
from the seventies, and is specially associated with the
names of Sir Joseph Hooker, at that time Director
of the Royal Gardens, Kew, of Sir Clements Markham
who occupied an important position at the India Office,
and with those of the collectors Collins, Cross and
Wickham. The success of the introduction of cinchona
to the East ten years earlier led Markham about 1870
to take up the question of the introduction of rubber to
India. The first step was marked by the preparation in
1872 of a report by James Collins, who had already
published an excellent account of the wild species
of rubber in 1868.

6 RUBBER AND

The story of the winning of the rubber seeds from
America is one full of romantic interest, and speaks
volumes for the enterprise and determination of the
collectors. The first seeds of Hevea to arrive at Kew
were probably those brought by Collins from the
Amazon in 1873. In 1875 Cross was shipwrecked
whilst on the way home with a consignment of Castilloa
plants and seeds. Nevertheless he managed to preserve
his precious collection and bring it safe to land. He
was sent out again to collect Hevea seed in 1877 and
was again successful. Although only a few of Cross's
Hevea seedlings were preserved, there must by this time
be a considerable number of trees growing in Eastern
plantations which are directly descended from the sur-
vivors of this consignment. Cross was also responsible
for the introduction of Ceara rubber to Kew about the
same date — a less difficult feat owing to the greater
powers of resistance possessed by the seeds of Manihot.

By far the largest and most important supply of
Hevea seeds to reach Kew was, however, that brought
home by H. A. Wickham in 1876. Wickham, who was
resident at the time in the rubber country of the Amazon,
was commissioned to supply seeds to the Indian Govern-
ment ; but the Brazilian authorities were naturally
opposed to the export of the seed, and it was a
remarkable chance which threw the required opportunity
in Wickham's way. An ocean-going steamer trading to
the Amazon was there abandoned by her supercargoes
without a return freight. Wickham boldly chartered

RUBBER PLANTING 7

the steamer on behalf of the Indian Government, and all
hands were pressed into the service of collecting seeds.
The cargo once aboard was passed by the port authori-
ties as botanical specimens, and upwards of 70,000 seeds
were thus safely transported to Kew. Less than
4 per cent, of these seeds, however, germinated. The
writer has Mr Wickham's personal assurance that these
seeds came from full-sized forest trees actually being
worked for rubber, which grew at a considerable distance
from the river on forest-covered plateaux some hundreds
of feet above flood-level. The often repeated statement
that the parents of the rubber plantations had their
origin in swampy ground liable to floods, may therefore
be taken to be entirely without foundation.

Although the Government of India paid all the
expenses connected with the introduction of Wickham's
seedlings, Ceylon was selected as the site of their chief
tropical nursery. A special garden at Henaratgoda, in
the low country near Colombo, was opened to receive
them, and here were set out some 2000 plants which
arrived in Ceylon in 1876 in 39 Wardian cases by the
s.s. Duke of Devonshire.

In the same year smaller consignments of plants of
Hevea brasiliensis were despatched from Kew to Burma,
Java, Singapore, and the West Indies. In 1877 plants
were sent to Mauritius and West Africa, and in 1878 to
Fiji.

Plants of Hevea Spritceana were first sent to Ceylon
in 1883, but they do not appear to have survived.

8 RUBBER AND

Castilloa and Manihot Glaziovii, Ceara rubber, were also
distributed by Kew to the same colonies at about the
same date.

Hcvea brasiliensis in Ceylon.

The principal nursery for the trees, which were to
form the origin of the planting industry, was however at
Henaratgoda, in Ceylon. Here flowers first appeared
upon the trees in 1881, and in the same year Dr Trimen,
the Director of the Botanic Gardens, commenced experi-
ments in tapping. The plantation was thinned out in
1882, and in 1883 2^° seedling plants were raised, most
of which were distributed in Ceylon. In 1884 there
were over 1000 trees at Henaratgoda, but it was found
necessary to thin the plantation again in 1885, an<3 we
read of 450 fine trees existing in 1887. In 1893 about
90,000 seeds were distributed to planters in Ceylon from
the Henaratgoda trees, and in subsequent years similar
numbers were available. Seeds were also distributed on
a considerable scale by the Ceylon Botanic Department
to Malaya and elsewhere, and it is curious to remark
that in recent years large consignments of seed have
been sent back from Ceylon and Singapore to America
and the West Indies for planting purposes. At the
present day about 40 of the original trees survive at
Henaratgoda, the largest being upwards of ten feet in
girth.

RUBBER PLANTING 9

Early Experiments.

Some of the earliest experiments in tapping planted
rubber trees were begun by Trimen at Henaratgoda in
1 888. One of the largest of the original trees was tapped
a few times in alternate years. Tapping consisted in
making gashes in the bark with a hammer and chisel,
in imitation of the methods employed in the Amazon
country. The recorded yields were as follows:

TABLE II
Yields of Rubber from one tree at Henaratgoda.

Year Ib. oz.

1888 I u|

1890 2 10

1892 2 13

i894 3 3

1896 3 o

Despite the fact that his first estimate of the probable
yield of a rubber plantation was a very low one accord-
ing to modern ideas, and although it was not considered
safe in those days to tap the trees at an earlier age than
10 or 12 years, Trimen foresaw that a very handsome
profit could be obtained from rubber planting, and
strongly advocated the cultivation of this product in
Ceylon in his report for 1888. In 1890 the Ceylon
Forest Department opened an experimental plantation
which was increased to some extent in subsequent years,
but on estates little planting took place during the
decade immediately following.

io RUBBER AND

Rise of the Plantation Industry in the East.

In Ceylon in the eighties, when the coffee plantations
were practically exterminated, some attention was paid
to the cultivation of Ceara rubber, but difficulties of
tapping soon caused this product to be almost entirely
neglected. From 1900 onwards further trials were made
with this species and with Castilloa, but it was soon
found that neither was so well suited as Hevea for the
conditions generally prevailing in the planting districts
of Ceylon. In fact, except in Africa, the fortunes of the
rubber planting industry are almost entirely bound up
with those of the last-named genus. Even in the Dutch
East Indies, plantations of Assam indiarubber (Ficus
elasticd) are now being cut down to make way for Hevea
brasiliensis. Our further remarks apply therefore mainly
to Hevea.

In 1890 about 300 acres had been planted with
rubber in Ceylon, and in 1900 about 1750 acres.
Planting continued steadily until 1904, when the area
was estimated at 11,000 acres, and then came the
historic rush into rubber which characterised the years
10,05 — 1907. In 1906 the first World's Rubber Exhibi-
tion was held at the Royal Botanic Gardens, Peradeniya,
and by the end of the year 100,000 acres had been
planted. The present area under rubber in Ceylon may
be estimated at upwards of 250,000 acres.

In the Federated Malay States the development of
the industry was even more rapid. In 1897 rubber

RUBBER PLANTING n

estates covered only 350 acres in Malaya. By the end
of 1906 the area of rubber plantations was practically
equal to that in Ceylon. In 1912 Wright estimated this
area to have increased to 420,000 acres. Whereas in
Ceylon a material proportion of the rubber has been
planted through existing tea estates, practically the
whole area under rubber in Malaya has been cleared of
virgin forest.

After Ceylon and Malaya, the next most important
centre for rubber cultivation is the Dutch East Indies.
It is estimated that 150,000 acres have recently been
planted in Java and 70,000 in Sumatra. The latter is
largely in the hands of English companies. The greatest
part of this rubber is Hevea, but considerable areas of
Ficus, Castilloa and Manihot also exist in Java.

Although India was the country originally proposed
for the site of a great planting industry, the early con-
signments of seeds — the first dates back to 1873 — did
not meet with much success, and little planting took
place before 1900. At the time of writing, however,
40,000 acres have probably been planted with Hevea in
Southern India.

In West Africa at the present time plantations
probably consist about equally of Hevea and of the
native Funtumia. In Angola and in Central and East
Africa, on the other hand, Ceara rubber is beginning to
be widely cultivated. In America, too, the natural
sources of rubber are being widely supplemented by
plantations. In Mexico large areas are cultivated

12 RUBBER AND

with Castilloa, and at the present time the Brazilian
Government is making great efforts to encourage the
establishment of Hevea plantations.

Wright gives the following estimate of the world's
planted acreage in 1912:

TABLE III
Acreage under Rubber in different countries.

Country Acres

Malaya 420,000

Ceylon 238,000
Dutch East Indies, Borneo and Pacific Islands 240,000

South India and Burma 42,000

German Colonies 45,000

Mexico, Brazil, Africa and W. Indies 100,000

This estimate is probably rather under than over the
mark. An estimate by Van den Kerckhove gives 220,000
for Mexico, 80,000 for Brazil, and 100,000 for Africa.
His total for the world is 1,131,000 acres in 1912.

Production from Estates.

A large proportion of the acreage described above
has been planted since 1906, and it will be readily
understood that the production of plantation rubber is
rapidly increasing, and is likely to increase at a still
more rapid rate in the immediate future. Indeed, at
the present time the increase is in geometrical pro-
gression, and for some years past the output of rubber

RUBBER PLANTING 13

both from Ceylon and from the Federated Malay States
has practically doubled every year. In fact, so far as
Ceylon is concerned, the following table shows that this
is an understatement of the case.

TABLE IV

Exports of Rubber from British Colonies in the East.

Y Ceylon exports, Malay Peninsula

tons exports, tons

1906 147 425

1907 248 1,036

1908 407 1,665

1909 666 3,340

1910 1,472 6,500

1911 2,900 11,000

1912 6,300 about 20,000

Lewton Brain in 1910 estimated the future yields for
Malaya as follows :

TABLE V
Estimated exports of Rubber from Malaya.

Year Tons

1911 10,950

1912 18,750

1913 26,550

1914 35,640
1916 65,000

There seems every reason for anticipating that these
estimates will be exceeded.

A million acres of rubber in full bearing may be
expected at a rough estimate to produce 150,000 tons of

i4 RUBBER AND

rubber annually. If the present increase in the rate of
consumption is maintained, it seems probable that the
whole of this amount will be required as soon as the
plantations can produce it. When this takes place, a
considerable reduction in the consumption of the lower
grades of wild rubber may be expected. Some reduc-
tion in the very large amount of reclaimed rubber used
by manufacturers may also occur when high grades of
fresh rubber are obtainable at a somewhat lower price.
Hitherto the increased demand has been such that with
the supplies of wild rubber practically stationary, or
even somewhat increasing, all the plantation rubber
available has been readily taken up, and prices have
been maintained at what may still be regarded as a
more or less artificial figure.

Variations in the Price of Rubber.

The history of prices is indeed remarkable, and the
factors which rule them are not always easy to under-
stand. Taking the price of fine hard Para as the
standard, the value of this commodity in 1871 was
about three shillings a pound. In 1878 the price was
only two shillings. This rose to 4/4 in 1883, and fell to
2/6 in 1885. From this point the rise in value was more
or less continuous until the price reached 5/8 in 1905.
In 1908, a year of considerable industrial depression,
the price fell to 2/9, but after this if rose very rapidly
until it reached the unprecedented figure of 12/9 in

RUBBER PLANTING 15

April, 1910. Much of this increase was probably
associated with the increasing demand for motor tyres.
After this, prices declined rapidly, and during 1912 the
price remained fairly steady, between 4/- and 4/6.

The price of the best grades of plantation rubber is
generally very close to that of hard Para. Hitherto,
however, Para has always retained a higher value than
the best plantation rubber, taking account of the fact
that the former contains upwards of 10 per cent, of water
more than the latter.

The amount of capital embarked in the rubber
planting industry is enormous. Wright estimates that
the nominal capital of companies registered in Great
Britain alone, between 1907 and 1911, exceeds
£90,000,000, of which about £60,000,000 is actually
paid up.

CHAPTER II

THE BOTANICAL SOURCES OF RUBBER

WE propose to give in the following chapter some
description of the different species of plants from which
rubber is obtained, and of the methods employed in
collecting the rubber from these plants in the wild con-
dition. It will be convenient to consider the various
species more or less in the order of their geographical
distribution. Before doing so we may briefly enumerate
the principal plants concerned according to their
botanical classification.

List of the Principal Rubber-yielding Species.

I. MORACEAE.

Castilloa elastica, C. Markhamiana.

Ficus elastica, F. Vogelii and other species.

II. EUPHORBIACEAE.

Hevea brasiliensis and other species.
Manihot Glaziovii, M. dichotoma, M. hep-

taphylla, M. piauhyensis and other

species.
Sapium Jenmani and other species.

Plate I

Fruits and Seeds of Rubber Plants

RUBBER AND RUBBER PLANTING 17

III. APOCYNACEAE.

Alstonia sp.

Carpodinus sp.

Clitandra sp.

Funtumia elastica, F. africana.

Dyera.

Hancornia speciosa.

Landolphia Kirkii, L. Dawei, L. owariensis,

L. Heudelotii, L. Thollonii, etc.
Leuconotis sp.
Mascarhenasia elastica.
Parameria glandulifera.
Urceola esculenta.
Willughbeia sp.

IV. ASCLEPIADACEAE.

Cryptostegia grandiflora.
Raphionacme utilis.

V. COMPOSITAE.

Parthenium argentatum.

AMERICAN SPECIES.
Hevea brasiliensisy Para Rubber.

About 21 different species of Hevea are found in the
Amazon region of North- West Brazil. Of these Hevea
brasiliensis is the most important, and furnishes the
highest quality of rubber.

L. 2

i8

RUBBER AND

Hevea brasiliensis is a tall and handsome tree, often
reaching a height of 90 feet, whilst the circumference
near the ground may exceed 12 feet. Commercially, its
most important feature is the bark, which reaches a
thickness of an inch or more in well-developed trees.

Fig. i. Hevea brasiliensis.
A. Young shoot. B. Inflorescence.

C. Flower.

In addition to containing an abundant store of latex,
yielding from 30 to 40 per cent, of rubber, the bark of
Hevea possesses an admirable consistency for the passage
of the various tools used in tapping, combined with a
remarkable faculty for recovering from the effect of

RUBBER PLANTING 19

wounds. The leaves are smooth, with three spear-shaped
leaflets, and are very variable in size; indeed, all the
characters of the tree are subject to marked variation.
In Brazil the shape of the leaves is considered to be
a feature by which good and bad varieties can be
distinguished. The variety introduced into the East
appears to be one of the best, although showing in its
turn considerable variation. In Brazil the leaves fall
from the trees about June, at the beginning of the
so-called dry season, and are replaced by new leaves
shortly afterwards. For a few weeks or days, therefore,
the trees winter with bare branches.

The trees introduced into Ceylon have encountered
there a reversed arrangement of seasons. On the
Western side of Ceylon, accordingly, leaf-fall takes place
in February.

The flowers appear shortly after the new leaves.
They are small and greenish in colour, and possess a
pleasant scent comparable with that of the blossom of
the lime tree. The male and female flowers are separate,
but are grouped in the same panicles. The fruits ripen
in about five or six months. Three large seeds, marbled
with brown and grey, are contained in a single fruit — a
hard woody capsule, which bursts open when ripe and
scatters the seeds to a considerable distance.

The structure and physiology of the bark of Hevea
will be dealt with in some detail in the following
chapters. We may proceed to describe the collection
of the rubber in the forests of Brazil.

2 — 2

20 RUBBER AND

The trees are said to flourish best on rich alluvial
clay swamps by the side of rivers. Tapping is carried
out between June and February, and is confined to trees
of 10 to 15 years of age and upwards. To each
seringueiro or collector are assigned from 100 to 150
trees, which are connected by a winding path, or
estrade, cut through the undergrowth. Tapping is per-
formed with a hatchet, shaped like a small poleaxe,
and the latex is collected in small cups of tinplate,
having a sharp edge which can be inserted into the bark.
Some days before the tapping proper is begun, the
trees are gashed high up with a long-handled hatchet, in
order " to make the latex ascend from the roots." The
actual tapping is done on alternate days. Beginning at
sunrise the seringueiro makes two rounds of his estrade,
the first in order to tap the trees and the second in order
to collect the latex. The first day's tapping consists of
a horizontal row of slanting incisions made with the
hatchet as high up as the operator can conveniently
reach. On subsequent days fresh rows of cuts are made
below the old ones, the bottom of the trunk being
reached on the average after about 35 tapping days.

The next operation is smoking, which is carried out
as soon as the latex is brought in, before coagulation
and putrefaction have time to assert themselves. A
smoky fire of wood, mixed with the nuts of certain
palms, is made beneath a kind of funnel-shaped chimney.
The latex is rotated in the smoke on the surface of a
wooden instrument which may be either rod- or paddle-

Plate II

Tapping Wild Hevea

RUBBER PLANTING 21

shaped. As each successive layer of rubber dries, fresh
latex is poured upon the surface until a large block or
ball of rubber is formed, which may weigh from 50 to
100 pounds.

The method above described appears to be nearly
identical with that which has been employed for
centuries by the natives of the Amazon valley. The
rubber obtained thereby is still adopted as the highest
standard of quality in the world's markets.

Economic Aspects of the Amazon Rubber Industry.

The country which produces Para rubber lies in the
States of Amazonas, Para and Acre. The pioneers of
the industry are constantly pushing further afield up the
different tributaries of the Amazon. When the country
has been explored and the presence of a suitable
number of Hevea trees ascertained, a grant of land is
obtained from the Government of the State, and after
the payment of certain taxes, the land becomes private
property.

The owner of the property is usually not himself a
large capitalist. In order to finance his enterprise, he
obtains a loan at a high rate of interest from a trader or
rubber merchant. Labour is chiefly imported from the
barren region of Ceara. The labourers often arrive at
the base of the expedition in a practically destitute
condition, and provision has to be made in advance for
food supplies, tools and transport. All supplies have

22 RUBBER AND

to be obtained from traders — naturally at high prices —
and all must be carried long distances by steamer to the
scene of operations. For working a seringal, or estate,
of 200 estrades, an advance of 180,000 milreis, or nearly
£10,000, including interest, may be required.

The paths of the seringal are practically sublet to
the individual seringueiros, who have to pay for their
food, tools, transport, etc., at high prices, together with
interest on the loan advanced to them for incidental
expenses, out of the value of the rubber which they
obtain. Since the rubber must be sold by the owner to
the trader, and by the trader to the exporting firm, very
little profit is generally left for the individual collector.
The inland freights, moreover, are very high, and an
export tax has to be paid on the rubber at the rate
of nearly 20 per cent, ad valorem.

The successful competition of the plantation industry
in other parts of the world has recently led to active
legislation on the part of the Brazilian Government,
with a view to removing as far as possible the handicaps
under which the wild rubber industry has hitherto
laboured. These fall mainly under the heads of expen-
sive labour, heavy transport rates and high export duty.
So long as the price of rubber remains high, the
Brazilian capitalist is able to pay for the high cost of
production plus the high freights and taxes, but as
soon as the price of rubber falls below three shillings a
pound, the pinch will be severely felt, not only by the
individual owner but also by the country in general, for

Plate III

m

» * 7«

few?

RUBBER PLANTING 23

the latter depends largely upon the export of rubber for
its revenue.

Special concessions are now being made to encourage
the introduction of foreign capital and the opening up
of plantations, by the granting of premiums and re-
mission of taxes. In addition, the Federal Government
is taking steps :

1. To encourage rubber collection and cultivation
by advancing money on easy terms, and by the offer of
premiums on new plantations.

2. To encourage industries for the manufacture of
rubber goods — also by the offer of premiums.

3. To help the regular workers and immigrant
labourers by the provision of special boarding estab-
lishments and hospitals and by the sale of stores at cost
price.

4. To reduce the cost of transport by opening
railways and improving the navigation of rivers.

5. To encourage the production of foodstuffs in the
Amazon Valley, in order to obviate the necessity of
transporting such materials for long distances.

6. To hold triennial exhibitions in Rio de Janeiro
of everything relating to the rubber industry of the
country.

And last but not least to open agricultural experi-
ment stations in different parts of the country1.

1 Abridged from the Handbook of the Third International Rubber and
Allied Trades Exhibition, New York, 1912.

RUBBER AND

Manihot Glaziovii.

This species, the source of Ceara rubber, extends
over a wide area in North-Eastern Brazil. It is adapted
to a drier climate than Hevea, and flourishes on a dry
and rocky soil up to an altitude of about 4000 feet The

A. Leaves.

Fig. i. Manihot Glaziovii.
B. Inflorescence. C. Female flower.

plant is comparatively shrubby, branching close to the
ground and rarely exceeding 30 feet in height The
bark has a hard surface, and readily peels off from the
trunk like that of a cherry or birch tree.

Tapping is therefore a more difficult process than in
the case of Hevea, although the latex and rubber

RUBBER PLANTING 25

obtained from the trunk are closely similar both in
quality and — relatively to the size of the tree — in
quantity. The raw rubber contains somewhat more
resin than Hevea rubber, and, however carefully pre-
pared, is quite distinguishable from the latter. The
latex coagulates without acid, on the mere addition of
water.

The leaves are generally three-lobed, and afford a
very dense shade, but the trees are markedly deciduous
and remain bare of leaves for a considerable period.
The seeds, which resemble those of the castor oil plant,
are very hard. They retain their vitality for a long
period, and do not germinate readily unless the shell
is filed through. The roots are tuberous like those of
the allied species Manihot utilissima, the cassava
plant.

Owing to the difficulties which attend the tapping of
the stem, the wild Ceara rubber is often tapped at the
roots or very close to the ground. The latex is then
simply collected in small cavities in the ground, opened
wherever the subterranean organs are discovered. The
cavities are usually lined with clay or leaves, but such
a method of collection naturally leads to the production
of a very impure form of cake or lump rubber. " Ceara
scrap" is obtained by gashing the stems with a knife.
The latex oozes out and is allowed to dry upon the
bark. It is then pulled off in strings, which are
either rolled up into balls or put into bags in loose
masses.

26 RUBBER AND

Other Species of Manihot.

In 1907 extensive reports were published in Germany
emphasising the importance of Manitoba rubber as dis-
tinguished from ordinary Ceara. This rubber was said
to be derived mainly from three species of Manihot —
M. dichotoma, M. heptaphylla and M. piauhyensis.
Formerly it appears to have been confused with the
produce of Hancornia speciosa. The seed of the above-
named species of Manihot has been widely advertised
for planting in tropical countries, but the small amount
of evidence at present available seems to show that they
are all less satisfactory than M. Glaziovii for plantation
purposes, Very large yields have been attributed to
young trees of the Manitoba species in Brazil. The
tapping of M. dichotoma is usually carried out with the
knife. When the latex is collected in vessels it begins
at once to coagulate. It is then moulded with the hands
into balls, which are usually pressed between rollers and
afterwards thoroughly dried. Manihot piauhyensis and
M. heptaphylla, on the other hand, are tapped at the
base of the stem, and the latex allowed to flow upon
the ground.

Castilloa.

Castilloa elastica is the source of the Ule rubber
of Central America and of the Caucho rubber of Peru.
The species extends from the South of Mexico to the
North of Peru, where it is separated from the territory

RUBBER PLANTING 27

of Hevca by the watershed of the Andes. In Panama
a different species, Castilloa Markhamiana, occurs, which
is considered less satisfactory as a source of rubber. It
is probable that it is this species which has been intro-
duced into the East. This may account for the somewhat
poor results which have been obtained with Castilloa in
British Colonies.

Fig. 3. Castilloa ehistica.

Castilloa has very large oval leaves, which are
arranged along both sides of special branches. The
latter fall off with the leaves, and the whole thus
simulates a compound leaf. The flowers are massed in
dense heads, and each gives rise to a single seed which
is white and comparatively small. The bark is very

28 RUBBER AND

hard throughout, and offers considerable resistance to
tapping. The latex tubes are larger than those of
Hevea or Manihot^ and are entirely devoid of the cross
partitions which characterise the early stages of the
latter. Partly for this reason more rubber is obtained
at a single tapping, but the trees must then be rested
for a considerable time before a fresh supply becomes
available. The trees occur naturally in small groups
along the banks of running streams from sea level to
an altitude of 1 500 feet, but they do not grow well in
marshy soil.

Tapping is carried out by making long slanting
cuts in the bark, sometimes extending right round the
tree in the form of one or more spirals. The flow of
latex is complete in 24 hours, and in some districts the
tree is then cut down in order to obtain the whole of
the available latex. The latex is acid in reaction, and
coagulation is effected by the addition of the alkaline
juice of certain plants or of a solution of soap. The
process is sometimes carried out in rectangular pits in
the ground lined with clay. The rubber thus obtained
contains numerous impurities. Owing to its greater
purity, the rubber which has dried on the tree fetches
a higher price.

Other American Species.

Hancornia speciosa, the source of Mangabeira rubber,
occurs in the South- West of Brazil and extends as far
south as Rio de Janeiro. It grows on plateaux at

RUBBER PLANTING 29

an elevation of 3000 to 5000 feet It is a small tree
with narrow leaves <jnd a drooping habit like that of
a weeping birch. The fruit is yellow and edible, some-
what resembling a plum. Tapping is carried out in
various ways similar to those adopted in the case of
Manihot, but it is said that all the different processes
are leading to the extinction of the plant. Coagulation
is generally effected by the addition of a solution of
alum or some other salt. The result is a wet rubber
which is not much valued in this country. The yield of
rubber is, however, said to be considerable, and the
plant appears to deserve closer attention than it has
hitherto received.

The same remark applies to some of the species of
Sapium, which grow at high elevations in Colombia and
Guiana. The Sapiums are large and hardy trees ;
nevertheless they have been largely exterminated in
their native forests by reckless tapping.

Other rubber-producing species of the Western
Hemisphere deserving of mention are Forsterionia
gracilis in Guiana and F. floribunda in Jamaica. These
are climbing plants comparable with the Landolphias of
Africa.

Guayule Rubber.

Before proceeding to describe the wild rubbers of
Africa and Asia, mention must be made of one other
American species of strikingly different habit from those
so far enumerated. This is Parthcnium argentatum,

30 RUBBER AND

the Guayule rubber plant of the deserts of Northern
Mexico. The Guayule is a small shrub, rarely attaining
a height of four feet or a diameter of more than three
inches. The plant contains no latex, but granules of
true rubber occur scattered through the tissues, especially
those of the bark. The plants are gathered as a whole,
and the rubber is obtained partly by a mechanical
process of grinding and partly by chemical extraction.
The exact processes employed are kept secret. Guayule
rubber was only first placed upon the market about
1903, when the demand for rubber was beginning to
outrun the supply. By the end of 1909 the extraction
of the rubber was said to be one of the most important
industries of Mexico. The supply is however already
diminishing, and this source of rubber can scarcely be
regarded as a permanent one.

AFRICAN RUBBERS.

The Lagos Silk Rubber, Funtumia elastica, formerly
known as Kickxia africana, is a handsome tree some-
what resembling a coffee plant when young. This
rubber first came into notice in the colony of Lagos
in 1894. The trees are tapped on a herring-bone system,
and the latex collected in a vessel at the foot of the tree.
In some districts the latex is coagulated by boiling;
this method yields an inferior rubber owing to the
damage often caused by excessive heating. A second
method is to pour the latex into a tank excavated in the

RUBBER PLANTING 31

trunk of a fallen tree. The strained milk is added from
day to day until the tank is full. It is then covered
with palm leaves and left for 12 to 14 days or more,
according to the season, until most of the watery
portions have either evaporated or sunk into the wood.

Fig. 4. Funtutnia elastica.
A. Branch. B. Inflorescence. C. Flower.

The rubber obtained has a dark brown colour externally,
with a paler section.

Funtumia is very susceptible to damage by in-
temperate tapping, and like other African rubbers, it
has been largely exterminated in many districts owing
to over-zealous collection. Recently plantations of this

32 RUBBER AND

species have been established in several parts of West
and Central Africa.

Although unsuitable for plantation purposes, the

Fig. 5. Landolphia Kirkii.
A. Leafy twig. B. Inflorescence. C. Flower.

various climbing species of the genus Landolphia are
still the chief source of wild African rubber. The

RUBBER PLANTING 33

Landolphias are widely distributed over the whole of
tropical Africa, extending from 16" degrees North
latitude to 23 degrees South latitude. They are found
in almost all the forest regions of this area, and include
at least ten species of valuable rubber-yielding plants.
Among the most important are Landolphia owariensis,
which occurs throughout West Africa and the Sudan,
L. Heudelotii in West Africa, and L. Kirkii and
L. Dawei in East Africa. Landolphia florida^ which
has also an extensive range, was known as a handsome
and sweet-scented flowering plant long before its com-
mercial value was recognised.

The rubber is exported in a great variety of forms,
often as small balls or sausages. These are formed by
winding up the strings of rubber which dry upon the
plants, when the latter are gashed with a knife.

Ficus Vogelii is another rubber plant widely dis-
tributed in West Africa and the Sudan. There have
been varying reports upon its produce, and it appears to
deserve further attention.

In all the above-named species the source of the
rubber is the stem. The so-called root rubbers of the
Congo and Angola are derived from the Rhizomes of
two semi-herbaceous plants Carpodinus lanceolatus and
Clitandra henriquesiana. The creeping underground
stems of these plants are about an inch in diameter.
The natives extract the rubber by rasping and then
boiling them in water.

In Madagascar rubber is obtained from other species

L. 3

34

RUBBER AND

of Landolphia^ and from a tree, Mascarhenasia elastica^
which is related to Funtumia, and resembles it in many
respects.

Fig. 6. Ficus elastica*

ASIATIC RUBBERS.

We now come to the tree which until quite recently
most people have been accustomed to regard as the
indiarubber plant par excellence. In its native home in
Assam and Upper Burma, Ficus elastica grows into an
enormous tree, which few people would recognise at first
sight as the familiar indiarubber plant of suburban front
rooms. The adult tree develops huge buttress roots,

RUBBER PLANTING 35

and the leaves on old branches are only three or four
inches in length. The fruits are little greenish-yellow
figs, half an inch long. They form one of the principal
foods of flying foxes.

In tapping,' cuts are made on the aerial roots and
even on the horizontal branches at intervals of a few
inches. The tree has to be climbed twice, once for
tapping, and again a day or two later in order to collect
the rubber. The dried rubber is torn away from the
cuts and rolled together into a ball. Eight or ten
pounds is said to be obtainable from a tree at one

tapping.

Ficus elastica also occurs in Java and Sumatra, and
both here and in Assam considerable plantations of it
have been established. In the Dutch East Indies,
however, it is being rapidly ousted by Hevea as a
plantation rubber.

Prior to the introduction of Hevea, the best rubber
of the Malay peninsula was obtained from species of
Willughbeia — large woody climbers, with stems six or
eight inches in diameter. Other rubber-producing
plants occur, but none of these are any longer of
much economic importance. Some of the species con-
cerned extend eastward to Siam, Cambodia and Cochin
China. Among these another climber, Parameria
glandulifera, has been described as one of the most
prominent. Species of Willughbeia also occur in
Borneo, where they possess some economic importance.
In New Guinea rubber is obtained from a species of

3—2

36 RUBBER AND

Ficus, and in Fiji from Alstonia plumosa. In all these
countries the development of plantations is rapidly
supplanting the collection of wild rubber.

Jelutong Rubber.

This rubber, called after the name used by the
natives in Borneo, is of a low type containing a very
high proportion of resin. It has, however, taken a
prominent place in the rubber market in consequence
of the recent high prices of purer kinds. Jelutong
rubber comes chiefly from Borneo and Sumatra, and is
derived from large forest trees of the genera Dyera and
Alstonia. These are abundant in certain districts,
mainly in swampy places, and may attain a circum-
ference of as much as 20 feet. Much damage has
already been done by native methods of collection, but
steps have recently been taken by the governments
concerned to safeguard the life of the trees. Large
factories have also been opened for producing purified
rubber by the use of resin solvents. Schidrowitz states
that the trees can be tapped 40 times in a year without
damage, and that as much as 100 Ibs. of latex can
be obtained from a single tree. The method of tapping
recommended is done with a gouge in the form of a
wide V.

The export of Jelutong in 1910 is said to have
exceeded 25,000 tons. The crude product contains
only 12 to 14 per cent, of actual rubber. There is also

RUBBER PLANTING 37

30 to 40 per cent, or more of water, and the remainder
is chiefly resin. This so-called rubber may be used
directly in combination with a certain proportion of
a purer grade for the manufacture of inferior classes
of goods, or the resin may be more or less completely
extracted by the use of solvents.

CHAPTER III

THE PHYSIOLOGY OF LATEX PRODUCTION

RUBBER is derived from a milky liquid, known as
latex, which occupies a special series of channels in the
cortex, or inner bark of a number of different species of
plants. The proportion of rubber contained in the
latex varies greatly in different species. In many latices
rubber is almost or entirely wanting, its place being
taken by various resinous substances. The majority of
the plants in which the latex contains a large proportion
of rubber are either trees, or shrubs, or woody climbers.
Before considering the origin and functions of latex,
we propose to describe in very brief outline the structure
and functions of those parts of a woody plant or tree
which are directly or indirectly affected when the latex
is removed by the operation of tapping.

The Structure and Functions of the Vegetative Organs.

What are known as the vegetative organs of a tree,
as opposed to the organs specially concerned with
reproduction, may be divided into leaves, stem and
roots. The functions of the roots — to take the last

RUBBER AND RUBBER PLANTING 39

mentioned organs first — are, firstly, to hold the tree
firmly upright by anchoring it in the soil; and secondly,
to absorb certain substances contained in the soil which
are essential for the nourishment of the plant Among
the most important of these substances, in addition to
water, are various compounds of nitrogen, phosphorus
and potash.

Before these substances can be utilised as food by
the different parts of the plant, it is necessary for them
to be altered and in most cases combined with the still
more important substance carbon, which is only obtained
through the leaves. One of the most important func-
tions of the leaves therefore is to absorb carbon from
the atmosphere in the form of carbonic acid gas. The
functions of the leaves however are by no means con-
fined to absorption. In addition we may compare the
leaves to so many minute kitchens or chemical labora-
tories, wherein the different ingredients of the food of
the tree are prepared and compounded into a form in
which they can be utilized and readily digested by the
cells that make up the roots, stem and other organs.
The energy required for these transformations is derived
from the rays of the sun ; and in orcler that the neces-
sary chemical changes may be properly carried out, it is
necessary for the leaves to be spread out in a position
where they are well exposed to air and sunshine.

We may next pass on to consider the functions of
the stem or trunk of the tree. The first of these is to
support the leaves in a position well exposed to light

40 RUBBER AND

and air; the second is to provide a channel for conduct-
ing the necessary mineral substances from the roots to
the leaves in a state of very dilute solution, and also for
conducting the elaborated food supply downwards from
the leaves to the roots. The liquid which thus circulates
through the different organs of the tree is popularly
known as the sap. A third function carried out by the
trunk or stem of most plants is the storage of reserve food
materials, which are accumulated in special cells, often
in the form of starch.

As it is from the trunk of the tree that rubber is
derived in the vast majority of cases, it is necessary to
enter rather more fully into the structure and functions of
this region. The trunk of a tree is well known to consist
of two main portions— the wood and the bark, including
under the latter term the layers described by botanists
as the cortex. The cortex may be roughly defined as
the softer internal part of the bark which adjoins the
wood. If the bark is stripped from the wood, separation
takes place at an extremely soft and delicate layer of
tissue known as the cambium. The cambium, as we
shall see later, is the seat of growth in thickness for both
wood and bark.

Channels for the conduction of sap occur both in the
wood and in the bark, and two entirely different streams
of sap are associated with these two regions. An up-
ward current of sap occurs in the outer part of the wood
through a series of minute vessels, in which the mineral
substances absorbed by the roots are carried to the

RUBBER PLANTING 41

leaves in a state of very weak solution. The perfected
food materials are carried down through definite chan-
nels, known as phloem tubes, in the inner part of the
bark, by a downward stream of sap which is entirely
independent of the upward stream. In species which
produce latex there is also present in the inner bark
a special system of minute vessels or tubes, which
contain an emulsion of rubber and other substances.
This system is closed, and is entirely separate from both
the above-mentioned sets of channels, having nothing
to do with either of them, although in position it is
closely associated with the phloem tubes which carry
the downward sap current. The upward and downward
streams of sap are found in all trees, but latex tubes
occur in only a comparatively small number of species.

A most important organ of the tree is the cambium.
It is in this layer of very delicate cells that the growth
and formation of new tissues are continually going for-
ward. On the inner side of the cambium fresh layers,
consisting of newly constructed vessels, fibres and cells,
are constantly being added to the wood. On the outer
side of the cambium, and consequently on the inner side
of the bark, similar new additions are constantly being
made to the latter. These additions to the bark provide
for the increased strain on the capacity of the conduct-
ing vessels, consequent on the general growth of the
tree; and replace the losses occasioned by ordinary
wear and tear, or in the case of cultivated rubber trees
by the tapping knife. In addition to the new channels

42 RUBBER AND

for the descent of sap, these additions include in certain
cases new vessels for the storage of latex. We shall see,
however, that in the majority of latex-producing plants,
the growth of the laticiferous system is independent of
the cambium.

The laticiferous system.

The channels, which contain the latex, occur in leaves,
stem and roots. They are already present in the young
seedling, and they may also occur in the fruits and
seeds. In the stem and roots these passages are usually
confined to the bark. The laticiferous channels may
arise in the bark in one or other of two distinct ways,
characteristic of different groups of plants, and the
resulting passages are distinguished as latex tubes and
latex vessels respectively.

Latex Tubes.

The type of channel which is characteristic of the
majority of latex-producing plants, although not of the
most important species from the point of view of
rubber-production, is known as a latex tube. So far
as is known latex tubes are never renewed from the
cambium. The tubes arise in the seedling in the form
of a small number of closed cells, which appear to be
capable of almost unlimited growth and extension. As
the seedling grows, these tubes also grow and insinuate
themselves between the growing cells of the cortex,

RUBBER PLANTING 43

keeping pace by branching with the increase in cir-
cumference of the stem. In Funtumia the whole of the
adult laticiferous system is derived in this way from
eight primitive cells which are already present in the
embryo. How such a system is renewed, after the
latex has been drawn off by tapping, does not appear
to be clearly understood. As a matter of fact some
months must elapse after a tree of Funtumia or Castilloa
has been tapped, before a full supply of latex can be
drawn off again, whereas in the case of Hevea and
Manihot tapping can be carried out daily without any
diminution of flow.

Latex Vessels.

In Hevea and Manihot, latex vessels are formed in
an entirely different manner by the fusion of rows of
cells derived from the cambium. These cells arise by
the division of cambium cells in precisely the same way
as any other cells of the inner bark. When first formed
they are more or less brick-shaped. They are nearly
square in section and their length is three or four times
as great as their breadth. The particular cells which
ultimately fuse to form the latex vessels are arranged in
the form of a network which is generally one cell thick.
The meshes of which the network is composed consist
of one or two rows of cells, and are elongated in the
direction of the length of the stem. The walls which
intervene between the separate cells of the same network

44 RUBBER AND

soon break down, and a more or less free passage
is established throughout. The interstices of the net-
work are occupied by the medullary rayst which are
groups of thin-walled cells running by way of the
cambium radially from the bark into the wood. The
medullary rays serve in part as conducting channels for
food materials between the wood and the bark, and
in part for the storage of reserve food supplies. The
whole laticiferous system consists of a series of such
networks one within the other, extending round the
stem. The space between two adjoining networks is
occupied by the cells and tubes of the phloem. From
the arrangement of the laticiferous vessels it will be
readily understood that their contents can flow more
easily in the longitudinal direction than transversely
round the stem.

Hevea. Gross structure of the bark.

If we begin an examination of the bark of Hevea
from the outside of the tree, we find first a brown or
grey layer of cork, which is generally thin in young and
untapped trees. The function of the cork is purely
protective. Secondly, beneath the cork there occurs in
healthy trees a thin dark green layer of living cells.
Discolouration of this layer may be taken as indicating
that the health of the tree requires attention. Thirdly
comes a granular yellowish or pinkish layer of tissue,
which makes up the greater part of the thickness of the

RUBBER PLANTING 45

bark. The granules consist of groups of thick-walled
stone cells. Owing to the small size of these groups,
they offer little obstruction to the passage of a tapping
knife, but they quickly turn the edge of a razor, making
the preparation of microscopic sections of the bark a
matter of some difficulty. The granular layer passes
insensibly into a very soft white layer, which imme-
diately adjoins the wood. These four layers make up
the bark as popularly understood. If the bark is
stripped from the tree, separation takes place at the
cambium, which is destroyed in the process of stripping.

Minute anatomy of Hevea bark.

The networks of laticiferous vessels in Hevea are
seen in transverse section to be separated in the radial
direction by about five rows of cells and other elements.
Many of these are actually the sieve tubes and com-
panion cells of the phloem. No radial connections have
been observed between the several networks, which
appear to extend completely round the stem, being
thus concentric and having no communication with one
another. The arrangement of the cells composing the
networks is seen more clearly in longitudinal sections.
In the younger networks, close to the cambium, the
remains of the cell-walls may still be seen partly block-
ing the interior of the vessels; in the older vessels the
transverse and most of the longitudinal walls between
adjoining cells become absorbed. Two stages in the

46

RUBBER AND

dissolution of the cell-walls are seen in Figs. 8 and 9.
Fig. 8 represents a tangential section of a network very
close to the cambium, whilst that shown in Fig. 9 is
older and further away.

In the seedling the nodes of the network may be
partly formed by tubular outgrowths of the cells which
meet and fuse together, thus recalling the behaviour of

Hevea transverse section of bark x 5. The tangential
lines represent groups of latex vessels.

latex tubes proper. Fig. 10 shows such a fusion in a
transverse section of the seedling. But in the secondary
laticiferous tissue derived from the cambium there is
hardly any outgrowth of this kind. The complete net-
work is laid down in situ.

In material which has been preserved in strong

Plate

Fig. 8.

Fig. 10.

Fig. ii.

Fig. 9.

Anatomy of Hevea

RUBBER PLANTING 47

Flemmings solution, the contents of the cells which
are about to form the latex vessels are distinguishable
almost immediately after they have been cut off from
the cambium (Fig. n). Their appearance and arrange-
ment at this stage is closely comparable with that of the
companion cells of the phloem. * Sometimes the nuclei
of the surrounding larger cells are to be observed closely
pressed against the walls next to the incipient latex
vessels, suggesting that the former may play some part
in providing materials for the contents of the latter.
The adult bark of Manihot has not been so closely
studied as that of Hevea, but the manner of formation of
the vessels appears to be closely similar in the two
cases. For further details, and for a full account of the
structure of the laticiferous system in the seedling, the
reader is referred to the papers of Dr D. H. Scott.

The effects of wounding tJte bark.

The further remarks in this and the following chapter
refer specially to Hevea brasiliensis unless otherwise
stated, for this is the only species of which the physio-
logy has been at all adequately studied. Even in the
case of Hevea further observations are much needed,
especially from the chemical side.

The evil effects of ringing the bark, i.e. severing it
by a cut which penetrates to the cambium and extends
right round the trunk, are primarily due to the inter-
ruption of the downward food current. Their food

48 RUBBER AND

supply being cut off, the starvation and ultimate death
of the roots is only a matter of time, if the ringing is
complete and permanent. Under these circumstances
the tree may linger on for several years, but all its vital
functions will be greatly impeded. Such ringing may
occur more or less completely as the result of injudi-
cious or unskilful tapping. Any cut or prick which
reaches the cambium cannot fail to sever a certain
number of the channels through which the sap passes
down to the roots; and it is probable that the weakening
effect of excessive tapping is often due as much to the
starvation of the roots as to the removal of the latex.
Any system of tapping which involves the cutting or
pricking of the whole circumference of the tree at one
time is bad from this point of view. In fact it must be
considered advisable never to tap more than one-third,
or at the most one-half, of the total circumference of the
tree at any one time.

Special stress has been laid by Fitting on the damage
caused by tapping too wide an area, and the views of
this observer undoubtedly carry great weight; although
some authorities consider that he has taken an unduly
serious view of the effects of such a process. Micro-
scopical examination shows that the functional con-
ducting tubes of the bark are mostly situated very close
to the cambium, inside the main layers of latex vessels.
Consequently the process of paring, if carried out with
sufficient skill, need scarcely affect the conducting tubes.
This may account for the fact that on some estates the

RUBBER PLANTING 49

spiral system of tapping has been continued for years
without any perceptible injury to the trees. Neverthe-
less, human skill is never perfect, and any false cut, even
if it just misses the cambium, may sever some of the
conducting tubes. This danger is clearly increased
when a large part of the circumference is tapped at
one and the same time. For this reason we do not
recommend the spiral system of tapping to those com-
mencing work on new estates.

Fitting has also studied the effect of tapping in
depleting the food supplies stored up in the bark. He
found a marked reduction in the amount of starch
present in the cells around and especially immediately
below the wound, after paring had been carried out for
some time. This fact suggests that food materials are
rapidly used up in the neighbourhood of the wounded
area. It may therefore be concluded that the removal
of large quantities of latex will tend to produce partial
starvation of other parts of the tree, an effect quite
distinct from any mechanical injury.

Renewal of bark.

The bark is constantly undergoing increase in thick-
ness owing to the activity of the cambium. As the
phloem tubes grow older their functions are given up,
and their place is taken by the younger elements within.
A considerable part of the older phloem and medul-
lary rays becomes converted into stone cells, which
L. 4

5o RUBBER AND

presumably serve a protective function. Active latex
vessels are distributed through a large part of the area
occupied by stone cells. Ultimately these also lose their
functions and dry up. Finally their remains are cut off
by layers of cork, and the rubber which they contain
is probably lost with the dry bark which rubs off from
the surface of the tree.

When the outer part of the living bark is removed in
the process of paring, the cambium and young bark
remaining are stimulated in a healthy tree to still
more active growth, and the tapped area is said to
undergo renewal. There is evidence to show that the
effect of this stimulus is not confined to the area actually
tapped, but that the bark of neighbouring untapped
areas is also stimulated to more rapid growth, provided
the rate of tapping is not excessive. The time required
by the bark for renewing such a thickness as will permit
of a repetition of the paring process, varies according to
circumstances. Factors which affect the rate of renewal
are the age of the tree, its relative size, strength and
state of nutrition, and any external circumstances which
modify the nutritive processes, such as climate, soil,
elevation and rainfall. Renewal is also affected by the
method of tapping adopted, and by the extent to which
the tree has been tapped. For although moderate tap-
ping stimulates renewal, excessive tapping hinders this
process, and the more heavily a tree is tapped — after
a certain rate has been reached — the longer will be
the period which must elapse before tapping can be

RUBBER PLANTING 51

repeated. It follows that there must be a certain
optimum rate of tapping for any given tree. Experi-
ence alone can determine this rate. A sound judgment
upon this point is perhaps the most important item in
the equipment of the successful rubber planter. Some
knowledge of the experimental work which has been
done by others, will, however, be found useful in setting
out to acquire the necessary experience.

The Functions of Latex.

The fact that the latex vessels are entirely separate
from the channels in which the food-bearing sap is
transported, gives rise to the natural question: what is
the use of these latex vessels to the tree, and what is
the precise function of the milky emulsion which they
contain? This is a point upon which we are still
very much in the dark. From the fact that the great
majority of trees of all kinds get on perfectly well
without latex, we are driven to the conclusion that this
substance is not essential for the life of the plant. It
is certainly the case that large quantities of latex can be
removed without causing any visible injury to the health
of the tree. The fact that the removal of latex stimu-
lates the tree to the production of large additional
quantities of this substance, having nearly the same
composition as the latex originally present, suggests
that the formation of latex cannot be regarded merely
as the excretion of a waste product. On the contrary,
the conclusion seems inevitable that latex is formed at

4—2

52 RUBBER AND

the expense of valuable food material, containing as it
does large quantities of carbon as well as a considerable
percentage of proteid material. There seems to be
no reason for doubting that the removal of latex causes
a sensible drain upon the supply of food available for
general growth.

It has been suggested that latex vessels serve as
additional channels for the transport of food; and it
has been stated that the phloem is poorly developed in
laticiferous plants. This is not the case in the prin-
cipal kinds of rubber trees grown upon plantations, all
of which possess a highly developed system of sieve
tubes. Other functions which have been attributed to
the latex vessels are storage of food, storage of water,
storage of excretory products, or a combination of
any two or more of the functions already named; or
finally protection against the attacks of insects and
other enemies. None of these suggestions, except the
last, appear to be based on any satisfactory evidence,
On the other hand, latex undoubtedly serves a pro-
tective function. Any area of bark which has been
entirely depleted of latex, owing to disease or other
causes, is usually soon riddled by boring insects. These
seldom or never attack bark in which a good supply of
latex is present. Whether this function can be regarded
as a sufficient cause to account for the separate evolu-
tion of such an elaborate system in several different
branches of the vegetable kingdom, is a question which
we may leave for the discussion of theorists.

RUBBER PLANTING 53

Composition of Hevea latex.

Fresh latex as it flows from the tree consists of a
fluid emulsion which closely resembles rather thin cream
in general appearance. The composition is also some-
what similar, except that the fats of the cream are
replaced by a different hydrocarbon. This hydrocarbon
has the empyrical formula C10H16, which is the same as
that of solid rubber. In the latex, however, the rubber
probably exists in a liquid form. In this case the
process of coagulation is either accompanied or followed
by solidification of the rubber globules. The liquid
hydrocarbon existing in the latex is believed to undergo
polymerisation to form true rubber by the coalescence
of several comparatively simple molecules into one of
a more complex character. In freshly drawn Hevea
latex the rubber globules are, on the average, approxi-
mately one-thousandth of a millimetre in diameter, but
many smaller globules also occur. In other latices the
globules may be somewhat larger, but their size pro-
bably seldom exceeds one ten-thousandth part of an
inch. The further study of such minute bodies is
naturally a difficult matter, but it is believed that the
rubber or simpler hydrocarbon is kept in emulsion by
the existence of a thin skin surrounding each globule,
and that this skin is either of a resinous or of a proteid
nature.

According to various estimates the composition of
the latex of Hevea is approximately as follows:

54 RUBBER AND

TABLE VI
Composition of Hevea Latex:.

Water 50 — 60 per cent

Caoutchouc 30 — 45
Resins i — 2

Proteids 2—3
Sugar -5

Ash -25

The latex from old trees usually contains a con-
siderably larger proportion of rubber than that obtained
from young trees. The composition of the latex is not
much altered by moderate tapping, but if tapping is
excessive the amount of rubber present may be greatly
reduced.

Coagulation.

Freshly drawn latex is alkaline in reaction. The
addition of a suitable amount of any kind of acid leads
to coagulation and to the separation of the rubber, with
most of the resins and proteids, from the watery and
soluble constituents of the latex.

According to the older view of coagulation, this was
supposed to be due to the bursting of the skins sur-
rounding the globules, followed by the coalescence of the
latter. Recent observations have shown that the globules
may persist in the coagulated latex. This fact seems to
support the view that the coagulation of Hevea latex
by acid consists in the formation of a network of coagu-
lated proteid, which entangles the rubber globules in its
meshes and contracts upon itself. The coalescence of

RUBBER PLANTING 55

the globules is only effected during the subsequent
pressing and working of the wet rubber. The question
of the extent to which polymerisation occurs during
coagulation appears to be still a disputed one.

Fresh latex also contains an oxydising enzyme which
leads to a darkening in colour on prolonged exposure
to the air. The enzyme may be destroyed by im-
mersing the coagulated rubber for a few minutes in
water at 80° C. and this treatment has been recom-
mended as a commercial process in order to obtain
light coloured rubber. Such treatment can be replaced
to some extent by thorough washing, and completely by
the use of vacuum driers, in which the rubber is rapidly
dried at a fairly high temperature.

CHAPTER IV

THE PHYSIOLOGY OF LATEX (continued] —

TAPPING EXPERIMENTS

Introductory.

THE examination of the living latex vessels in situ
is a matter of extreme difficulty. On the other hand,
the removal of the bark from the tree is followed by
immediate collapse of the vessels, by the loss of a large
part of their contents and by marked changes in form.
Our knowledge of the physiology of the laticiferous
system is therefore almost entirely derived from a study
of the behaviour of the trees during the process of
tapping. Experiments in tapping Hevea brasiliensis
were carried out by the author at Henaratgoda, Ceylon,
during the years 1908 — 1912. These experiments were
begun in consultation with Dr J. C. Willis and Mr M.
Kelway Bamber, of whom the latter also collaborated in
the earlier experiments.

Throughout these experiments a particular system of
tapping was adopted. This was done, not because the
system itself was regarded as an ideal one, but for the
sake of uniformity, in order that there should be a

RUBBER AND RUBBER PLANTING 57

reasonable basis for comparison between different ex-
periments. For ordinary use on estates a somewhat
different system is to be recommended. Such a system
will be described in a later chapter.

The system employed in the experiments was as
follows. The tree was first marked with three vertical
/ lines. Two of these lines were placed exactly on oppo-
site sides of the tree, and the third divided the bark on
one side between the two first lines into equal areas.
From a point on the middle line rather more than a
foot above the level of the ground, two lines were ruled
slanting upwards at an angle of 45° to meet the lateral
lines, thus marking out a large V on the surface of the
tree. Above the first V other V's were traced at inter-
vals of a foot. The number of V's tapped simultaneously
was three in the majority of the experiments. In other
experiments, designed for the study of special points,
six V's were tapped at once on the same side of the
tree; but where no statement is made to the contrary,
it is to be understood that the number of V's under
operation at any one time was confined to three.

In the positions indicated by the V's thus traced,
grooves were cut in the bark to a suitable depth for
tapping the laticiferous tissue without damage to the
cambium. The points of the V's were joined by a
shallower vertical groove serving to conduct the latex
to a cup placed at the foot of the tree to receive it.
The above processes constitute the first day's tapping.
Subsequent tappings consist in removing a thin shaving

RUBBER AND

THI
AR

RD
E A

FOU

AR

RTH
EA

of bark from the lower side of each V, in order

to reopen the latex vessels
which become plugged with
coagulated rubber during the
intervals between successive
tappings. By this process the
whole of the outer bark be-
tween the V's is gradually
removed in the form of thin
shavings. When this has been
done the tapping of the first
area of bark is said to be
completed. In the majority
of experiments tapping was
A R then continued by the similar

A\R E/A treatment of the corresponding

area of bark on the opposite
side of the tree, and when this
_________ _ __ in turn was finished a similar

Fig. 12. Shows the tapped area was tapped immediately
above the first area. Similar
tapping of a fourth area im-
mediately above the second
area completed the treatment of as much bark as could
conveniently be reached from the level of the ground.
In the more prolonged experiments tapping was then
continued on the renewed bark of the first area1.

1 During the first three years tapping in the main experiment with
70 trees, the spur pricker was used in combination with paring. This

SEC

OND

areas as they would appear on
the bark if removed from the
tree and spread out flat.

RUBBER PLANTING 59

Further details with regard to tapping will be found
in Chapter VI ; but it may be pointed out here that the
method described is known as an excision method, as
opposed to methods of incision in which the bark is
merely pricked with a pointed instrument or gashed
with a hatchet or chisel. The latter is the method
generally employed in collecting wild rubber, whereas
on plantations excision is the rule.

Wound Response.

If a tree of Castilloa or Funtumia is tapped, and the
wounds are reopened after an interval of a few days, or
if the bark is again tapped after a short interval in the
neighbourhood of the original cuts, little or no latex is
obtained at the second tapping. The bark is milked
almost dry at a single operation, and the latex tubes
are not completely refilled for several months1. In
the case of Hevea and Manihot, on the other hand,
a good yield is again obtained after an interval of only
a single day. These facts have long been known to the
collectors of wild rubber. The Hevea trees in the forests
of Brazil are tapped repeatedly during a single season,

method was given up about the middle of 1911, owing to the accumulation
of evidence that the use of the pricker led to damage of the trees. The
result of subsequent tapping in which the paring knife only was used, con-
firmed this impression and led to a general increase of yield.

The use of the pricker may be regarded as having accentuated the
damage done to the bark of the trees tapped at shorter intervals.

1 If indeed they ever recover. It is equally likely that much of the
latex obtained at later tappings is derived from new latex tubes budded off
from the old ones.

60 RUBBER AND

whereas in Central America it has frequently been the
custom to cut down the Castilloa trees in order that
the whole of the available rubber may be obtained at
one time.

With the establishment of plantations, opportunities
for more precise observations soon arose. Among the
earliest experiments dealing with "wound response"
were those of Willis and Parkin, who first made use of
this expression. These experiments were carried out in
Ceylon and may here be recorded on account of their
historical interest.

In 1897 Willis tapped a number of Hevea trees of
about two feet mean girth at intervals of a week with
the following result.

TABLE VII
Willis. Average yield per tree (dry rubber).

Ounces Ounces

First week 73 Fourth week -80

Second week 1*48 Fifth week -67

Third week -97 Sixth week -52

More elaborate experiments were carried out by
Parkin at Peradeniya in 1899, and the result of one of
these is recorded in the following table.

TABLE VIII
Parkin (Latex, six Trees).

March 25 ... 6ro c.c.

30 ... 105-5

April 6 ... 220*0

12 ... 208-5

15 ... 255-5

20 ... 290-0

25 ... 276-0

May i ... 253-0 c.c.

6 ... 264-5

13 .- 275-0

20 ... 255*0

26 ... 262'O

June I ... 328^0

6 ... 449-0

RUBBER PLANTING 61

It will be seen that after 14 tappings made at inter-
vals varying from three to seven days (average interval
5 -6 days), the yield had increased by over 600 per cent.
The increased yield thus recorded was ascribed to the
effect of wound response.

There seems to be little doubt that the increase
recorded by Parkin was an exceptional one, and that
rather too much weight has been laid on the phenomena
observed. It is quite possible that part of the increase
was due to climatic conditions, and this view is sup-
ported by the -rainfall returns during the period of the
experiment, which have fortunately been preserved.
They are as follows:

TABLE IX
Rainfall at Peradeniyay 1899.

Inches

March 5-42

April 18-40

Inches
May 7-59

June 1074

Reasons for the increase of yield on tapping.

It is possible that the immediate response to tapping
is partly due to a reduction in the viscosity of the latex,
which is thus enabled to flow more freely. When part of
the latex is removed from the vessels by tapping, the in-
ternal pressure of the latter is reduced and the remaining
latex is diluted by the entrance of sap from the surround-
ing cells. The pressure in the surrounding cells may
also be increased owing to the irritation consequent upon

62 RUBBER AND RUBBER PLANTING

wounding. It is a fact that the proportion of caoutchouc
in the latex often falls off rapidly during the first few
tappings. The important point to be observed, however,
is that the yield shows no diminution for a considerable
period in spite of continued tapping even at daily inter-
vals. Table XI shows the yields of dry rubber from 70
trees tapped at Henaratgoda, beginning in June 1908.

The trees were taken in groups of ten, numbered
from I to VII respectively, and the average interval in
days between successive tappings in the case of each
group was as follows:

TABLE X
Average intervals between tappings.

Group I. II. III. IV. V. VI. VII.

Days 1-275 2-225 3-35 4-425 5-525 6-55 7'325

The interval aimed at was an even number of days
in each case. The actual excess was due to the fact
that it was not always found possible to tap on the
appointed day.

The tappings at longer intervals extended of course
over a longer period of time than those at shorter
intervals, consequently the climatic conditions are not
identical in the case of the results recorded in different
columns of Table XL Nevertheless it will be observed
that the variations in yield throughout the whole
experiment were comparatively small.

In other experiments a larger initial increase in
yield was observed. In such cases the results resemble

TABLE XI. First 40 Tappings. Total Rubber from 10 Trees
tapped at intervals of \ — 7 Days (nominal].

(Weights in grammes ; circumference in inches.)

I. II. III. IV. V. VI. VII.

Total Circumference of each Ten Trees.

362

359

313

366

336

402

39^

194

143

155

149

117

135

114

159

194

237

146

175

169

224

185

197

140

146

225

188

231

148

138

235

158

22O

194

235

133

197

190

141

241

172

168

174

152

190

174

245

141

194

184

189

150

190

182

142

202

170

183

143

155

183

126

197

160

169

156

152

209

166

167

1 10

177

139

161

I87

150

174

159

161

1 66

194

160

I96

170

141

155

140

208

171

I96

140

151

150

163

223

219

202

144

151

171

181

203

IIO

179

J88

158

134

149

243

169

144

133

150

179

185

167

153

145

153

137

147

169

209

192

140

196

177

188

186

87

133

136

134

176

291

154

116

103

158

202

170

237

184

129

123

154

1 80

177

208

156

105

1 10

127

141

190

203

148

145

97
106

153
150

170
148

180

200

292
230

!

128

82

151

171

163

188

105

92

146

1 66

192

198

154

134

102

1 10

168

251

205

100

^33

112

1 80

151

1 86

197

'55

III

66

167

165

208

141

126

98

211

148

159

181

133

114

67

159

152

138

148

'54

98

86

140

159

163

190

143

102

59

137

181

207

160

128

94

98

139

151

157

174

"5

120

109

131

148

161

130

92

132

147

120

158

158

98

80

90

141

158

141

130

85

105

152

160

184

139

92

IO4

118

153

160

155

106

88

123

65

181

164

147

104

Si

5,9M

4,885

6,124

6,494

6,707

7,725

5,953

16-3

13-6

•9-5

177

2O'0

19-2

15-0

1 An interval of u days between the s8th and 29th tapping of row I.,
and between the i4th and I5th tapping of row II.

64 RUBBER AND

those of Parkin more closely. It must be remembered
also that the method of tapping employed was entirely
different from that of Parkin, who used an incision
method pure and simple, and did not reopen the same
wounds. The result of all such experiments may be
summarised as follows. With any moderate method of
tapping, carried out at nearly equal intervals, which
may vary in length from 24 hours up to 10 days, the
yield per tapping rises rapidly to a point at which it is
subsequently maintained, subject to certain variations
the nature of which will be considered later on.

Duration of yield.

With moderate and careful tapping no limit can at
present be set to the period during which a similar yield
will continue to be obtained from Hevea. By the end
of April 1912, the tapping of the same seventy trees
had been continued without intermission for nearly four
years. The annual yields obtained are summarised in
the following table:

TABLE XII

Yields calculated to Ibs. of dry rubber per acre.

Row

Year I. II. III. IV. V. VI. VII.

1908 (7 months)... 950 590 485 390 335 345 240

1909 ... 890 600 480 380 360 340 265

1910 ... 900 540 380 380 370 300 255

1911 ... (3501) 700 500 620 580 500 370

1912 (4 months)... — 180 145 220 240 220 165
Average annual

yield for 4 years ... 770 650 500 500 470 425 325

1 For 4 months.

RUBBER PLANTING 65

The result is here calculated in the form of the
weight of dry rubber which would be obtained from an
acre planted at the same distance as the actual trees
under experiment. After continuous tapping for nearly
four years the trees, especially those tapped at the longer
intervals, were yielding rubber in considerably larger
quantities than the average amount for the first year.
It must be pointed out that the trees in question were
upwards of 25 years old, and had not been regularly
tapped before the experiment began. They are also
very closely planted, namely at a distance of only
12 x 12 feet.

Here we appear to have evidence of a very real and
prolonged response on the part of the trees to certain
stimulating causes. Among these, two definite stimuli
may probably be distinguished, firstly the removal of
the latex, and secondly the irritation due to the wound-
ing of the bark. In the case of young and vigorously
growing trees a further reason for the increase in yield
is apparent, namely the rapid increase in the total
volume of the bark. In the case of the trees used
in the foregoing experiment, the average increase in
girth was less than one inch per annum, so that the
increase in volume of the bark was very small in com-
parison with the amount present at the beginning of
tapping. In trees growing under more favourable con-
ditions the increase is often three or four times as great.
In the case of young trees planted at wide intervals no
limit can at present be set to the period during which

L- 5

66 RUBBER AND

a gradual increase in yield may be shown, so long as the
tapping is not severe enough to cause definite injury.

Relation of yield to volume of bark.

The evidence already given is sufficient to show that
the amount of latex which can be removed from a
Hevea tree in one year, must be very large in comparison
with the quantity which was present in the vessels prior
to the commencement of tapping. In further illustra-
tion of this point we may take the case of an excep-
tionally large and vigorous tree, the yield from which
was separately recorded for a considerable period.

This particular tree is one of those originally planted
at Henaratgoda in 1876. Its girth at three feet from the
ground was 102 inches in December 1908 when the ex-
periment was begun; and it had increased to 115 inches
in December 1911, at which date the available records
come to an end. The tree therefore continued its
normal rate of growth of upwards of three inches per
annum throughout the whole course of the experiment.

The tree was tapped daily on the three-V system
described above, and in the space of a little more than
two years, four similar areas of bark had been com-
pletely tapped. The renewed bark on the first area
was then retapped, and was nearly completed at the
end of December 1911. During this last period tapping
was carried out daily during alternate months, with
monthly intervals of rest. The yield of dry rubber was
as follows:

No. of

produced,

Tapping,

Tappings

grammes

grammes

153

19,794

130

185

19,744

107

137

15,832

116

125

22,827

183

RUBBER PLANTING 67

TABLE XIII
Yield of dry rubber in three years from a single tree.

Total Rubber Average per
No. of
Section
I.
II.
III.
IV.
I. on renewed bark

not completed 150 30,508 203

In three years the total yield was nearly 240 Ibs.
of dry rubber. This was contained in about 70 gallons
of latex, or nearly 20,000 cubic inches. The total
area of the bark tapped during this period was about
10,000 square inches. The thickness of the laticiferous
bark was about half an inch, so that the volume of the
bark actually subjected to tapping was about 5000 cubic
inches. It is by no means an easy matter to estimate
the volume of latex vessels contained in a given volume
of bark, owing to the marked shrinkage of the former
when the bark is removed from the tree. It will be safe
however to assume that the total volume of the latex
vessels is not more than one-tenth of the total volume
of the bark, and most writers upon the subject have
given a considerably lower estimate. We have therefore
obtained in three years 20,000 cubic inches of latex by
tapping an area of bark which did not contain more
than 500 cybic inches of latex at the beginning of the
experiment. The problem before us is to account for
the remaining 19,500 cubic inches of latex.

5—2

68 RUBBER AND

The tree is about 80 feet high, and at about ten feet
from the ground it divides into three main branches
each about four feet in girth. In comparison with the
girth at the base of the trunk, the crown of the tree is
by no means extensive. In fact the volume of the
bark per foot of altitude probably falls off rather than
increases as we pass upwards, since although the total
circumference of the branch system increases, the thick-
ness of the bark rapidly diminishes. We may therefore
assume with some degree of confidence that the total
volume of the laticiferous system of the whole tree does
not exceed 5000 cubic inches, and is probably very
much less. Even if this very liberal estimate be adopted,
the whole system must have been emptied twice over
in the space of three years. At the end of this period
the vessels were still full of latex, and the freedom of
flow had increased rather than diminished.

Origin of Latex.

What is the source of this very large supply? It has
been suggested that the latex may be manufactured in
the leaves and pass down the tree to the wounded area.
Now Hevea is a deciduous tree and in Ceylon drops the
whole of its leaves in February or March. There may
be an interval of nearly a month between the loss of
the old leaves and the time when the young leaves
become fully functional. Hence, if the leaves represented
the chief source of the latex supply, we should expect
the yield of latex to be reduced almost to nothing
shortly after the fall of the leaves, if tapping be carried

RUBBER PLANTING 69

on without intermission. We shall presently see that
there is some falling off in yield about this period, but
that the reduction is not nearly so great as would be
expected on the theory of the origin of the latex in the
leaves. Moreover the composition of the latex in the
leaves differs considerably from that in the stem.

During the experiment the tree was steadily in-
creasing in girth, and new latex vessels were constantly
being added to the bark by the activity of the cambium.
The amount of bark tissue thus added in three years
over the area actually tapped was nearly equal to
the amount removed, but in other parts of the tree
much less. The new latex vessels contained in the
renewed bark are therefore only responsible for a com-
paratively small proportion of the latex obtained. The
greater part of the latex still unaccounted for can only
have been produced in one way, and that is by the
active secretion of latex in existing laticiferous tissue.
In fact we arrive at the important conclusion — not by
any means universally accepted — that the laticiferous
tissue of the bark is an organ for the manufacture of
latex as well as for the storage of latex.

There is evidence that this process of manufacture
is specially active in the immediate neighbourhood of
the wounded area. In an experiment carried out on
29 trees of an average girth of 26 inches, the whole of
the outer bark on one side was removed to a height of
six feet by tapping on a six-V system for a period of
only six months. Tapping was immediately continued

70 RUBBER AND

by a similar system on the other half of the tree.
The cuts were twelve inches apart, and, after the first
day's paring had been carried out, each further cut
except the lowest was apparently draining an almost
isolated patch of bark, of an average area of 216 square
inches. In this case the average thickness of the latici-
ferous bark was not more than a quarter of an inch, and
on our previous assumption the average volume of the
latex vessels contained in one of the isolated patches
of bark, could not have been more than 5j cubic inches.
The yield in six months from the lowest cut but one
was 55 cubic inches of latex, more than 10 of which
were drawn off during the first month of tapping.

There must nevertheless be a considerable move-
ment of latex from untapped bark towards the seat of
tapping. It was calculated that the largest day's yield
from the old tree previously described would have drawn
off the whole of the latex from a distance of at least
three inches from the tapped surface. As the tubes are
never completely emptied, there was probably an actual
flow from at least double this distance. In the case of
this particular tree the flow continued for several hours,
whereas in the majority of trees the cut surface becomes
blocked by coagulated rubber in less than one hour
after tapping. The structure of the laticiferous system
shows that movement of the latex will take place more
readily in the vertical direction, but that a lateral flow is
also possible. In the older networks a gradual trans-
ference of latex may take place over an extensive area.

RUBBER PLANTING 71

Seasonal variation.

Some idea of the variations in the flow of latex at
different times of year on the Western side of Ceylon
may be obtained from the following table, which em-
bodies the results of three years' continuous tapping
of the 70 trees already described as having been tapped
at different intervals by groups of ten. Tapping was
carried out during the last seven months of 1908, so that
by the beginning of 1909 the trees may be supposed to
have been responding freely to the influence of tapping.
By taking the average of three years we can eliminate
to some extent the effect of different stages of tapping.
This is necessary because, at least when the tapping
intervals are short, the yield is greatest soon after a
particular area is begun, and falls off when the bark on
that area is becoming exhausted. Row I is omitted
because it was only tapped for a few months during 191 1.

TABLE XIV
Average yields per tapping, 1909 — 1911 (grammes).

Average

II.

III.

IV.

V.

VI.

VII.

II.— VII.

January

83

96

in

141

148

144

120

February

74

89

no

127

133

127

I JO

March

61

83

106

H3

H5

96

April

(57)

72

92

H5

116

88

00

May

63

70

97

118

107

93

91

June

60

75

109

137

120

129

105

July

77

7i

102

134

136

129

108

August

84

72

104

130

I29

112

105

September

84

74

U3

135

141

137

114

October

84

77

116

(HO

160

138

119

November

9i

89

125

151

167

153

129

December

87

84

128

161

171

158

131

72 RUBBER AND

It appears that on the average the yield per tapping
is lowest in April and May. This yield rises continuously
until December and then steadily falls off again. The
increase from April to December on the average of these
three years, and taking the average result from tapping
at a number of different intervals, does not fall far short
of fifty per cent.

The seasonal variation in yield is clearly associated
to some extent with the climatic conditions at different
seasons, as may be seen on comparing it with the follow-
ing table which shows the average monthly rainfall at
Henaratgoda for the three years 1909 — 1911.

TABLE XV

Rainfall at Henaratgoda^ A verages 1 909 — 1911.

Rainy

Rainfall

Rainy

Rainfall

Month

days

(inches)

Month

days

(inches)

January

4

i'54

July

10

8-88

February

i

•6 1

August

9

7-04

March

6

3'95

September

5

2-91

April

6

4'43

October

16

24-86

May

10

6-69

November

16

11-81

June

12

9'oi

December

9

7-99

It will be observed, on comparing Tables XIV and
XV, that the season of highest yield follows shortly after
the season of greatest rainfall. In countries subject to
a prolonged dry season the variations in yield are much
more marked. The following table shows the monthly
crops of dry rubber harvested during 1912 on a well-
known' property in South India.

RUBBER PLANTING 73

TABLE XVI

Stagbrook Rubber Co. Crop of dry rubber in Ibs.

Month

Crop

Month

Crop

January

2345

July

2256

February

nil

August

2809

March

nil

September

5871

April

nil

October

9087

May

1205

November

14088

June

2514

December

18000

More than half the total crop was harvested in the
last two months of the year.

Some relation can also be traced between the yield
and the rainfall at different seasons in any given year.
It seems clear however that the variation at Henaratgoda
is also affected by .other factors. The highest yields are
obtained in November, December and January, just
before the time of leaf fall. There is then a rapid
falling off, and the yield remains low until August, that
is to say during the whole time of the formation and
ripening of the fruits. This is what would naturally be
expected on general principles, although the differences
are perhaps less marked than we might have been led
to anticipate. Whatever the function of rubber may be,
there can be no doubt that its formation constitutes a
tax on the food supplies of the tree, whilst the latex
removed in tapping contains other materials of possible
nutritive value. We should expect the available sup-
plies of food material to be greatest just before the fall
of the leaves, since these are engaged up to the last in

74 RUBBER AND

food production, and give up part of their organic
contents to the tree before they drop to the ground.
In April and May, on the other hand, the formation of
fresh leaves, flowers and fruits has successively drained
the resources of the tree, so that these must be at a
comparatively low ebb. We find, accordingly, that the
percentage of caoutchouc is highest in December and
January, and lowest in May and June.

Variation in yield of individual trees.

It is well known that rubber trees possess a marked
individuality as regards the amount of latex which can
be drawn from them. Tapping coolies, if left to them-
selves, soon discover these differences, and confine their
attention to the best-yielding trees. The differences are
often great, and to a large extent independent of the
girth of the trees. Among a group of 29 trees of
uniform age tapped daily, the highest and lowest
average yields for the first 30 tappings were respectively
1 66 and 8 cubic centimetres. The circumferences of
these two trees were 52 and 32 inches respectively, and
they were not the largest and smallest trees of the
group. The yield per inch of bark removed was in the
ratio of 317 to 25, or more than 12 to i. Such
differences afford good grounds for anticipating that
markedly increased yields could be got from plantations
derived from the seed of trees selected for their high
yielding capacity. As we shall point out at greater

RUBBER PLANTING 75

length in Chapter v, the selection of seed-bearers may
be expected to play an important part in the future
development of the rubber-planting industry.

Tapping Intervals.

The increased yield associated with wound response
is clearly manifested when the interval between suc-
cessive tappings is anything between one and ten days1.
The longest interval over which this effect can persist is
not known, and would doubtless be found to vary in the
case of different trees. It was observed, however, in the
case of a very large tree which was tapped daily, that,
when daily tapping was renewed after an interval of a
month during which tapping had been suspended, the
first day's yield was much smaller than the average,
and was followed by a rapid increase on the days
immediately following. A longer interval than a week
between successive tappings is not likely to enter into
the calculations of the practical planter. Which is the
most profitable among intervals shorter than seven days,
i.e. which will lead to the largest permanent yield, is a
question that requires to be made the subject of further
discussion and experiment.

The view generally accepted at the present time is
that, with a view to obtaining the largest possible yield
without permanent damage to the tree, tapping should
proceed at such a rate that the paring of the whole area

1 Except perhaps in the case of very young trees.

76 RUBBER AND

of bark accessible from the ground occupies not less
than four years. Under these circumstances it will not
be necessary to touch the oldest renewed bark until the
beginning of the fifth year. The system of tapping is
generally so arranged that this object is achieved by
tapping either daily or on alternate days. There is
evidence however that, in the case of old trees closely
planted — and close planting is the rule on the older
plantations — a better result can be obtained by in-
creasing the interval between successive tappings.

In this connection reference may be made to
Table XII, which shows the annual yields from 70 old
and closely planted trees, divided into groups of 10,
which were tapped at different intervals. The rate of
tapping of the different groups was such that the
original bark would be exhausted at approximately
the following rates.

TABLE XVII
Time occupied in tapping original bark.

Row I. II. III. IV. V. VI. VII.
Years 24 6 789 10

Although Group I gave the highest total yield, the
bark was so much injured by the rapid tapping that
no further extraction of latex was possible after May,
1911, and it is anticipated that some years must elapse
befone tapping can be resumed. All the other groups
show increased yields in 1911 and 1912, but the relative
increase is greater in the case of the groups tapped at

RUBBER PLANTING 77

longer intervals. In illustration of this difference, details
are here given of the yields during the first four months
of 1912.

TABLE XVIII

Yield of dry rubber \ January to April, 1912.

Row

II. III. IV. V. VI. VII.

Number of tappings 42 32 24 20 16 14
Yield of dry rubber

(grammes) ... 3,164 2,216 3,873 4,072 3,765 2,862
Yield per tapping

(grammes) ... 75 70 161 203 235 202

The above figures may be compared with those in
Table XI. A more convenient comparison is given
however in the following table.

•

TABLE XIX
Yields in grammes per inch of circumference.

Average Average yield per Average yield per

tapping tapping per inch tapping per inch

interval of bark, ist 40 Jan. — Apr., 1912 Diflfer-

Row (days) tappings (grms.) (grammes) ence

II. 2*6 *34 *2i —*I3

III. 3-9 -49 -22 --27

IV. 5-1 -44 -44 o

V. 6-5 -50 -60 -io

VI. 7-8 -48 -58 -io
VII. 9-0 -37 -51 -14

It is to be observed that January to April is usually
a period of comparatively low yield, whilst the first 40
tappings of groups V, VI and VII extended over the
whole of the period of highest yield. The increase in

78 RUBBER AND

the later yields per tapping is therefore certainly not
exaggerated by the conditions of the experiment.
Under these conditions, after the tapping has been in
progress for three and a half years, it appears that the
longer the interval between successive tappings — up to
an interval of about a week — the greater is the yield per
tapping.

If we consider the total yields of rubber per month,
this yield is greatest at first from the trees tapped at
more frequent intervals. The relative yield from the
trees tapped at longer intervals however gradually
increases. After three and a half years' continuous
tapping, the yield from trees tapped once a week may
become as great as or greater than that from trees
tapped at any shorter interval. A discussion of the
practical importance of these conclusions may be
reserved for a later page.

Overtapping.

The results just recorded naturally lead on to a
discussion of the amount of tapping which can be
performed without injury to the tree. Overtapping may
be considered either in relation to the excision of bark
or to the removal of latex. It is usual to discuss only
the former kind of loss in this connection, but there is
no doubt that a tree can be overtapped by pricking
only, without any removal of bark tissue. In many
systems of pricking the damage done to the bark is at

RUBBER PLANTING 79

least as great as in the case of paring, and with the best
possible method of incision some damage is inevitable.
Removal of latex without injury to the bark is in fact
impossible, but even if this were possible there would
still be a limit to the amount of latex which could
be extracted without injury to the tree. For the manu-
facture of latex necessarily uses up a certain amount of
food and energy, and the supply of these in the tree is
not unlimited.

The problem of the physiological effect of paring
upon the tree is therefore a complicated one. In addition
to the rate of removal of the bark, both the amount of
latex taken from the tree and the frequency of this
extraction have to be considered. In the experiment
with seven groups of trees described above, Group I
and some of the trees of Group II may be said to
have been overtapped, because at the time when the
whole of the outer bark had been removed up to the
greatest height convenient for tapping, the renewal of
the first area tapped was still imperfect. This result
was no doubt partly due to defects in tapping, but with
the most perfect tapping there must be a limit to the
possible rate of removal of the bark which will permit
of proper renewal.

Let us assume a system by which the whole of the
outer bark is removed to a certain height in a given
period. Then if at the end of this period the bark of
the area first tapped has not renewed sufficiently to
allow of a second tapping, it is clear that the proper

8o RUBBER AND

period for renewal has been underestimated. From the
point of view of bark-removal the trees have been over-
tapped. This is the criterion of overtapping which is
most often adopted in practice. It would probably be
better however to extend the idea of overtapping
somewhat further, and to recognise that it is possible
for a tree to be overtapped owing to the excessive
removal of latex, although there may be a considerable
area of untapped bark still available for tapping.

In the case of young growing trees planted with
plenty of space, the yield of latex may be expected to
increase steadily from year to year, so long as the bark
is preserved in good condition. The ideal rate of
tapping may be defined as that rate which is associated
with the greatest increase in yield as time goes on. Any
quicker rate may consequently be regarded as involving
overtapping from the point of view of latex removal.
In the case of the old trees at Henaratgoda, the rate of
tapping associated with the greatest increase in yield
proved to be considerably slower than the rate required
for a degree of bark renewal which would generally
be regarded as complete.

Yield at different levels of the trunk.

The bark is thickest near the base of the tree, and it
is here that the greatest flow of latex is obtained. On
29 trees tapping was carried on by six V cuts placed
each one foot below the next, the lowest cut being one

RUBBER PLANTING 81

foot above ground level. Continuous paring for nearly
six months produced the following yields of latex from
the different cuts.

TABLE XX
Yields of latex at different distances from the ground.

Height above ground Yield of latex,

level, feet cubic centimetres

6 16,607

5 18,281

4 18,773

3 22,353

2 25,998

i 67,942

The lowest cut of all gives a very much larger yield
than any of the others, owing to the fact that it drains a
larger area of bark, and one which is in free communica-
tion with the covering of the roots. The five upper cuts
are more nearly comparable with one another. These
show a steady slight increase in yield in passing down
the stem. The latex from the lower cuts also contained
a slightly higher percentage of rubber than that from
the upper cuts.

Incidentally these figures afford further evidence in
support of the conclusion that the bulk of the latex
obtained is manufactured locally. If the latex passed
down in large quantities from the upper part of the
trunk and then flowed laterally into the tapping area,
we should expect a larger flow from the topmost cut
than from the cuts immediately below it. As a matter
of fact the reverse is the case.

L. 6

82 RUBBER AND

The yield of latex at six feet from the ground was
rather more than three-fifths of the yield at two feet in
the case of this particular experiment. The only reason
for confining tapping to the lowest six feet of the trunk
is therefore one of convenience. Profitable yields could
doubtless be obtained at a considerably greater altitude,
but this would entail great loss of time in tapping, owing
to the necessity of climbing the tree.

Effect of tapping on the composition of the latex.

The increase in flow associated with wound response
is accompanied by a reduction in the concentration of
the latex. Hence in terms of latex the increases in
yield during the early stages of tapping would be larger
than those shown in the various tables in the present
chapter, which refer to yields of dry rubber. Table XXI
illustrates this fact. This table is the counterpart of
Table XI, except that the entries refer to percentages of
rubber in the latex, instead of to weights of dry rubber.
Table XXI further shows that the falling off in concentra-
tion is much more rapid when the tapping intervals are
small than when they are larger. After a certain period,
which is longer when the intervals are longer, a more or
less permanent concentration is reached, which persists
for an indefinite period, but is also subject, as in the case
of the yield of dry rubber, to seasonal variation. This
more or less permanent concentration is considerably
higher in the case of the trees tapped at longer intervals.

RUBBER PLANTING 83

TABLE XXI

First 40 Tappings. Percentage of Rubber in Latex. Average
of 10 Trees in each case tapped at intervals of I — 7 Days.

I. II. III. IV. V. VI. VII.

No. of Tapping
i

Tfcto

J<to

497
49'4
46-0

38-9
39*o
36-8
37-6

36-5
35'2
35'2
34'3
32*1
32-8
30 '6
29-5
28-8
27-9

2r5
26-3

27-2
26-3
26-4
25-9
25-9
267
28-5
28-9
30-0
29-8
30-2
30-8
3o-2
26-3
277

3°'4
3i'2

29'9
27-2
28-0
28-6

1 Circu

359
50*0

45'°
41-2
40-4
36-1
38-2

44 '4
42-2

37-9 .

30-8
317

29^

25^
30-3
31-4

T
30-6
27-2
3o-i
29-4

29*0
29-0

27-6
32-2
29-5
29-4

29*6
32?'8

30-0

30-2
31-6

31-0
29-5

mferei

313

46^2
4ox>
40*0
37'4
34'9

317

34-8

32*5
35'o
33'4
34'9
35-6
32-6
34'6
32-8
35'2
33*5
3i7
327
32-6
30-1
33'2
26*0
33-6
35-c

35?2

31*1

33'9
32-3
33-8
35'5
34*5
33*o
34'5
3i-3
32-3
34*o

ice of t

366

50*0
39'4

36-5
34'3
357
35'2
36-3
36-2
36-8
36-0
38-8
39'5
36-3
41*0
37'6

39-

37'6
38-8

35'5
39'2
38-5
38*2
38-2

37*3
39-6
4ro
39'4
39'6
39'5
40-4
38*0
41-4
397
40'3
4i'5
41*0

43'3

'ach T

336

?

43*4
37?*

?

367
36-8

39'3
38-5
37-2

38-9
35'o
377
34'8

39'9

40'2

38-1

37-9
38-6
39-0

40*0
387
38-3
40-0
37*0
4O'o
42-4
39'3
39'o
407

40-5
42-9
39'i
42'3
40-8

397
39*5
43'5
40-5

en Trt
402

?

43'i
41-8

39'6
39-0
39-2

4i*3
41*5
40-6

44'4
42-5
41-2

41-3
36-3
40-4
38-6
40'0
38-0
40'0

43'3
40-8
40-8

42'3
40-4
42-9
40'3
40-3
43-8

42-5
45*5
42-5
42-2
407

43'°
46-5
39-0
39'5

40'2

35'8
37'9

'es.
30

53'5
41-0
36-8
35'9

?
377
367
36-1

377
38-6
40-2
33'4
39*9
37'o
41-0
36-6
38-0

37'5
42-0
38-0
417
41*0

4i-5
38-0

43'9
45'3
42'3
39'°
4i'S
39-6
41-4
41-0

39*5
36-6

38-4
37'i
36-1
34-3

2

c...

g

7

8

Q...

IO

1 1 ....

12

T-3

14.

1C.1..

16

17...

18. .

IQ .

2O

21

22

23...

24...

2C

26

27

28

2Q

SO

<U...

•52

»*...

34...

-3C

36...

77...

78

7Q.

40...

6—2

84 RUBBER AND

Thus the averages of all the concentrations determined
during this experiment, from 1908 to 1911, were as
follows :

TABLE XXII
Percentages of rubber in latex.

I.

II.

III.

IV.

V.

VI.

VII.

1908

32-1

33'6

35'5

39'3

38-5

40-9

40-4

1909

30-1

31-0

33*5

37-6

37-8

39-0

36-9

1910

28-3

29-5

31-2

35*5

37*4

37'4

377

1911

—

29-3

33'3

35'9

37'5

38-0

36*0

The seasonal variation in the concentration of the
latex during prolonged tapping are similar to those
observed in the total yield of dry rubber. The pe'r-
centage of rubber was found to be generally highest
about January and lowest about June. This fact
supports the view that the yield depends upon nutrition

TABLE XXIII
Percentages of rubber. Monthly averages^ 1909 — 1911.

II.

III.

IV.

V.

VI.

VII.

Av.

January

34'o

34*5

39'5

4°'3

41-4

40*2

38'3

February

32-8

33'9

37'9

39*2

40-2

37-6

36-9

March

287

34'i

367

37-0

377

37*o

35'2

April

257

337

36-8

38-4

37-6

35'9

347

May

26-1

30*0

347

35-6

35'3

3i'4

32-2

June

2 1 '2

30-2

33'9

35'5

36-2

35 '9

32-1

July

28-6

29-2

31-5

36-0

34'9

36-3

327

August

29-4

32-6

357

36-6

37'i

39-0

35'i

September

30-9

36-3

36'9

38-1

37'5

37'4

36-2

October

31-8

32-6

'37*2

36-3

41-1

36-6

35'9

November

3I-9

32-2

36-1

37-8

38-1

38-6

35-8

December

32'6

32-9

38-6

39'9

40-9

37'4

37-0

Average

29-5

32*5

36-3

367

38-2

37 -o

35-1

RUBBER PLANTING 85

as well as upon the supply of moisture, since otherwise
the concentration might be expected to be highest in
the dry season and lowest in the wet. There is however
no evidence of an increase in concentration during dry
weather.

The concentrations here recorded were determined
by dividing the weight of dry rubber by the volume of
the latex, a method which gives values slightly too low
throughout.

The dry rubber obtained in this experiment from the
second to the sixth tapping of each group (samples A),
and again after tapping had been in progress for four
months (samples B) was analysed for ash, resin and
organic matter. As regards ash, practically no differ-
ence was found between the product of earlier and
later tappings. The proportion of resin showed a slight
falling off in the product of the later tappings, especially
in the case of the more frequent intervals.

The organic matter in the two series showed
differences of considerable interest. In the groups
tapped at shorter intervals the organic matter from the
later tappings showed a distinct increase, whilst in the
groups tapped at longer intervals the reverse was
the case. The following purely tentative explanation
was put forward to explain these differences. "If we
suppose that some part of this organic matter represents
the raw material from which the rubber is formed, then,
in the case of daily tapping we may suppose that the
drain upon the resources of the tree is at first greater

86

RUBBER AND

than it can cope with, but that later the bark reacts
more perfectly to the stimulus of tapping, and pro-
duces the raw material faster than the cells can convert
it into caoutchouc. In the case of tapping at longer
intervals, on the other hand, we may suppose that
the stimulus to manufacture rubber leads to an accumu-
lation of this material in the latex tubes, which is only

TABLE XXIV
Analyses of rubber from earlier tappings.

Ash

Per cent.
o-33
0-23
0*27
0-31
0-31
0-23
0-23

Sample

Organ

No.

Resin

matte

Per cent.

Per cei

i A

2 '04

0-84

2 A

273

0-83

3A

1-92

0-94

4A

2*16

0-86

5A

i'75

0-93

6A

2'6o

I'll

7A

2-19

1-09

Chemical test

Organic

Indiarubber by

matter

difference

Per cent.

Per cent.

0-84

96-79

0-83

96*21

0-94

96-87

0-86

96-67

0-93

97-01

I'll

96-06

1-09

96-49

Analyses of rubber from later tappings.

Chemical test

Sample

Organic

Indiarubber by

No.

Resin

matter

difference

Ash

Per cent.

Per cent.

Per cent.

Per cent.

i B

178

1-59

96-35

0-28

2 B

r84

i'43

96-43

0*30

3B

179

i*43

96-53

0'22

4B

i '93

071

97-14

0'22

5B

1-67

0-52

97-67

O'I4

6B

2 '40

0-44

96-94

0'22

7B

2-19

0-63

96-95

0-23

RUBBER PLANTING 87

partly removed by the e.g. weekly opening of the
vessels, and that this concentration... inhibits the further
production of raw material. In other words, tapping
stimulates the tree both to the production of the raw
materials for rubber and to the conversion of these into
rubber. With frequent tapping the raw materials are
produced faster than they can be converted; with less
frequent tapping the reverse is the case1." It is scarcely
necessary to point out that the whole subject requires
further investigation from the chemical standpoint.
The actual figures obtained in the analyses are given
in Table XXIV.

General considerations affecting yields.

Given a uniform and moderate system of tapping,
the yield from a Hevea tree should increase steadily
with its age and girth. Too drastic tapping will
certainly reduce the rate of increase of yield, and may
even lead to a falling off in the absolute yield of latex
and of rubber. On the other hand, there is reason to
believe that the yield after a given number of years will
be greater from a tree which has been regularly tapped
in moderation than from one which has been left un-
tapped. It should be observed, however, that the
definite experimental evidence upon this point is very
limited. Assuming that moderate tapping stimulates
the tree to increased activity in the production of latex,

1 Circulars R. B. G. Peradeniya, Vol. v. No. 16.

88 RUBBER AND

it should be the aim of the planter to discover just that
rate of tapping which will lead to the most rapid
increase of yield under the conditions affecting each
particular field.

Just as in the case of many other physiological
functions, the yield of latex at any given age would
appear to be controlled by a number of limiting factors.
The system and rate of tapping represent one such
factor. Others are the available space, soil and water
supply, and climatic conditions generally. These con-
ditions severally react upon what is probably the most
important factor of all, namely the individual character
of the tree.

The rate of increase of yield will be reduced if the
trees are planted too closely. But the most profitable
number of trees which can be borne by any given acre
at any given age, is a problem which can only be solved
by prolonged trial and experience. When the soil is
rich, more space is required for the full development of
the trees than when the soil is poor. Similarly, more
space is required at any given age at low than at high
elevations.

The condition of the water supply seems to have an
even more immediate effect upon the yield of latex.
Where the water level is close to the surface of the soil,
as in parts of the Federated Malay States, large yields
are obtained at an early age. When the water level is
deep below the surface, the roots may not penetrate
to the requisite depth for some years, and during this

RUBBER PLANTING 89

period the yield is more dependent upon the seasonal
rainfall. From old trees which have penetrated to the
water level, larger and more continuous yields are
obtained. This seems to be the case with the old
trees at Henaratgoda, where the water level is upwards
of 25 feet below the surface.

Resting Periods.

A question which is frequently asked concerns the
necessity or otherwise of resting periods. This also is
a question upon which definite experimental work is
required before a positive conclusion can be arrived at.
It has been recommended that tapping operations
should be suspended during the period of leaf-fall, and
this advice seems to be based upon reasonable grounds.
In climates such as those of South India and the north-
east side of Ceylon, the yield is found to be reduced
almost to nothing during the prolonged dry season. In
these climates the year is divided of necessity into a
season of tapping and a season of rest.

From the available evidence it seems probable that
in countries not subject to periods of prolonged drought
continuous moderate tapping is likely to be more profit-
able than alternate periods of rest and severe tapping.
The continuous method is also distinctly more convenient
in connection with the working of a labour force. The
theoretical advantage of the continuous method is asso-
ciated with the habit which the tree seems to acquire of
manufacturing a steady supply of latex.

90 RUBBER AND

The effects of tapping on the tree.

Moderate tapping seems to encourage not only
increased latex formation but also an increased rate of
growth in thickness over the area tapped. It seems
probable that this increase must take place at the
expense of the growth of other parts of the tree. So
long as the only recognisable effect of this kind is a
reduction in the quantity of seed produced, no harm is
done from the planter's point of view. It may even be
suggested that artificial removal of the young fruits
might prove profitable, if it could be carried out at a
small expense, as leading to the conservation of food
supplies in the tree.

Severe tapping has a reverse effect in every way. If
the trees are tapped to excess, growth is checked, and in
particular the proper renewal of the bark is interfered
with. The latex moreover becomes poor in quality and
contains a smaller percentage of caoutchouc. Most
serious of all is the effect upon the general health of
the plant. The tree may be so weakened that it is
unable to withstand the attacks of fungus diseases,
which would not have been able to gain a footing if
the tree had been preserved in a condition of perfect
health. Canker and similar diseases seldom attack the
trees unless the latter are either overtapped or very
closely planted.

RUBBER PLANTING 91

Summary.

In Hevea brasiliensis as grown under plantation
conditions, repeated tapping on a moderate system at
intervals varying from one to ten days leads to an
immediate steady increase in the yield of latex and
rubber obtained at each tapping. In the case of young
and vigorous trees, this increase may continue for an
indefinite period, subject to certain seasonal variations.
The increase is found to take place even with daily
tapping if the system adopted is such as to allow four
years for the renewal of the bark. In the case of old
trees, closely planted, after tapping has continued for
some time, the yield from tapping at longer intervals
increases relatively to the yield from tapping at shorter
intervals.

This fact may be regarded as one aspect of the more
general phenomenon that moderate tapping leads to
a steady increase in yield, whilst overtapping ultimately
leads to a relative falling off in yield. The amount of
excision which constitutes overtapping depends upon
the conditions and upon the individuality of the
particular tree.

The bulk of latex which can be extracted in a year
is probably often quite as great as the total volume
which all the latex tubes of the tree could contain at
any one time. Although the latex can pass gradually
from one part of the tree to another, especially in
the vertical direction, the greatest part of the latex

92 RUBBER AND RUBBER PLANTING

removed is probably secreted at no great distance from
the wounded area.

Under the comparatively uniform conditions of the
climate of Western Ceylon, the yield of latex at certain
seasons may be nearly twice as great as at other
seasons. Seasonal differences of yield are partly deter-
mined by climatic conditions, but probably also in part
by the quantity of food materials available in the tree.

The yield from different trees of the same age and
girth varies greatly. A difference of 1000 per cent, is
not at all uncommon.

The yield is greatest near the foot of the tree, and
decreases gradually on passing upwards. In all prob-
ability the yield is roughly proportional to the volume
of the bark at any given level.

The percentage of rubber in the latex shows
variations similar to those displayed by the total
yield. The percentage is highest during the period of
highest yield. Severe tapping leads to a marked falling
off in the percentage of rubber present.

It may be concluded that in practice the rate of
tapping should be reduced either

(1) if the bark is being used up at a greater rate
than one quarter of the available amount annually, or

(2) if the concentration of rubber in the latex falls
much below thirty per cent, or

(3) if the yield of latex fails to show an increase
over the amount obtained at the corresponding period
of the preceding season.

CHAPTER V

HEVEA. PLANTING OPERATIONS

Choice of situation and soil.

THE hardiness of the Hevea rubber tree in the
different countries of its adoption has been the occasion
of some surprise. In Ceylon the trees have made re-
markably good growth in situations where, in the early
days of their introduction to the country, botanical
experts would never have supposed them capable of
growing with permanent success. Anywhere in moist
climates within ten degrees of the equator Hevea will
grow, though not luxuriantly, even in rocky situa-
tions up to 2500 feet elevation. Here it may be seen
entering into competition with the still more hardy
tea-bush in its power of making the best of unfavourable
circumstances. It will also grow in comparatively dry
districts, if adequately protected from wind. The soil
at Henaratgoda is remarkably poor ; nevertheless, as we
saw in the last chapter, phenomenal yields have been
obtained there from old trees. On such a soil, however,
the early growth of the trees is generally slow. In fact

94

RUBBER AND

the appearance of the Henaratgoda trees during the
first few years after their introduction, led to the
erroneous conclusion that on rubber estates in Ceylon
tapping could not profitably be begun until the trees
had reached an age of ten years at least.

It is on rich alluvial soils in the moist low country
that the tree makes its most rapid growth and gives
its earliest and heaviest yields. The low-lying alluvial
soils of the Malay Peninsula and the light and fertile
volcanic soils of Sumatra have alike shown themselves
to be admirably suited for the growth of Hevea. Even
these soils would not be reckoned particularly rich
according to the ideas of farmers in a temperate
climate. Some idea of the relative proportions in
which the different constituents occur in different soils
may be obtained from the following table of analyses.

TABLE XXV

Analyses of Rubber Soils.

Organic matter and

combined water ... 24-080

Nitrogen 0-667

Potash 0-131

Phosphoric acid ... 0*025

Lime 0*284

B

5-12

0-27

0*26

0*072

trace

7-8

0-154

0-046

0-031

0*040

D

4-20

0-099

0-274

0-114

2-468

A is an alluvial clay from the Malay Peninsula,
analysed by Kelway Bamber.

B is a Sumatran soil analysed by Schidrowitz.

Plate V

RUBBER PLANTING 95

C is the "cabooky" soil at Henaratgoda, Ceylon,
analysed by Bruce.

D is an analysis by Dyer of soil at Rothamsted
upon which wheat had been grown continuously for
fifty years without manure. The low percentages of
organic matter and nitrogen are to be associated with
the exhaustion produced by this continuous cropping.
Nevertheless this soil is still much richer in mineral
constituents than either of the three examples of
tropical soils. Even the Malay soil, rich as it is in
organic matter and nitrogen, is very poor as regards
phosphoric acid, and by no means rich in potash. In
spite of such deficiencies the warm moist climate of
the tropics gives rise to an abundant growth of vege-
tation.

In short, it may be asserted that Hevea can be
grown to a profit on almost any soil in the latitude
of Ceylon up to an elevation of 2000 feet, provided
the rainfall exceeds 75 inches a year, and provided a
situation is chosen which is not exposed to strong
winds, especially at the dry season of the year. On
the other hand, the richer the soil and the lower the
altitude the better, provided that on swampy lands
good drainage be provided. The best test of a soil —
much better than the test of chemical analysis — is the
character of the vegetation growing upon it. If the
growth of forest over a given area is luxuriant, other
conditions being favourable, then a good growth of
rubber is assured when the forest is cleared. And if

96 RUBBER AND

it is intended to plant rubber where other agricultural
products are already established, the fact of a good
return from crops of any other kind may be taken as
an earnest of good crops of rubber to come.

Throughout the tropics good forest land is always
best for planting if it is obtainable, and it is greatly
superior to grass land or land which has already been
cropped. The greater part of the rubber in the Malay
Peninsula has been planted where virgin forests have
been cleared, and in every country this is one of the
most frequent conditions. In Ceylon a great deal of
rubber has also been planted through existing fields
of tea, in Sumatra on old tobacco land, and in Java
amongst various other products. Where such methods
are adopted the cost of clearing and weeding are
debited to the original crops, but the growth of the
rubber must be expected to be considerably slower than
on an original clearing opened for rubber alone. The
latter method is therefore the one to which we shall
devote the most attention.

In selecting the site for a rubber estate several other
considerations besides soil and climate demand atten-
tion. Foremost among these is the question of
transport. Rubber is a commodity of which the bulk
is relatively small in comparison with its present value,
but the weight of the produce from a large estate is
by no means a negligible quantity. The conveyance
of food and other necessities for the labour force in-
volves a considerable amount of transport, and it must

RUBBER PLANTING 97

not be forgotten that heavy machinery will have to be
introduced when the time comes for building the factory.
Ready access to a railway, canal or seaport is therefore
desirable, and a special feeding canal or road may have
to be constructed. The development of railways has
now proceeded to a considerable extent in Ceylon, Java
and the Federated Malay States, as well as in India.
In the low-lying coastal regions of the Malay Peninsula,
water transport is extensively adopted on the canals
which are necessary for purposes of drainage. Roads
are being widely constructed, and the system of these
in Ceylon is particularly extensive and excellent. Here
too signs are not wanting that the now universal
bullock cart may one day be largely replaced by the
motor lorry.

Land Tenure.

In Ceylon crown land is sold outright by auction,
and is subject to a reserve price. Temple lands in the
Kandyan country can be leased for a period of fifty
years. A large proportion of the land suitable for
rubber cultivation has now been disposed of in this way,
or is already in private hands. In most other rubber-
producing countries the land is held on lease from the
government, and the latter often retains the right to
resume possession if the lessee fails to open up the land
at a certain rate, or otherwise to conform to certain
regulations laid down.

L. 7

98 RUBBER AND

Clearing.

The heavier the forest the greater will be the
expense for clearing, but in the same proportion the
growth of the rubber may be expected to be better.
The trees on the land seldom pay for working, and
much fine timber is thus wasted, only so much being
saved as is required for buildings on the estate. Clearing
is often carried out on contract. In some cases only the
undergrowth is cleared and burnt, the larger trees being
ringed and left to die. At the present day this practice
is seldom adopted. Not only is it much better to fell
and burn everything growing upon the land, but if
possible all tree stumps should be extracted and no
dead wood should be left to rot upon the ground. In
some cases no doubt the cost of such operations is
prohibitive, but the immunity from the attacks of white
ants and root diseases, which can be obtained in no
other way, is worth considerable extra expense. On
level land, moreover, it may be possible, if stumps are
extracted, materially to reduce the cost of weeding and
cultivation by the use of agricultural machinery during
the early stages of growth of the rubber. Probably the
only real objection to the use of machinery in this
connection where the conditions are suitable, lies in
the conditions of labour management. A considerable
labour force is necessary both for opening the estate
and for harvesting the rubber. In the interval between

RUBBER PLANTING 99

these operations — extending over at least four years —
the principal work available for the labour force is
weeding. On large estates which are opened gradually,
so that the first fields may be already in tapping before
the whole of the original forest land is cleared, this
objection does not apply. In such cases stumping and
the use of agricultural machinery may be recommended
wherever the lay of the land is suitable. When we
consider the way in which even heavier timber is re-
moved by far more expensive labour in newly opened
districts of North America, the fact that simple stump
hauling machinery has scarcely been introduced into
the tropics is certainly remarkable. Its introduction
may be expected to lead to considerable economy and
immunity from disease.

Nurseries.

In planting up a rubber estate, nursery plants not
less than twelve months old are usually employed.
Hence the establishment of nurseries is one of the
first operations to be undertaken. The best planting
land also makes the best nursery, and a site should
be chosen where the soil is as rich as possible, well
drained and well sheltered from wind. The nursery
should be close to the fields where the plants will
ultimately be required, in order to reduce transport
as much as possible. In countries subject to a pro-
longed dry season some artificial shade may be

7—2

ioo RUBBER AND

necessary, but the heavy shade of trees is to be
avoided, chiefly on account of the damage which may
be done by the drip from the leaves in wet weather.
The soil should be well dug and laid out into beds
of any convenient size. The most important point is
the allowance of ample space for the growth of the
plants. The seeds should be planted at a distance of
not less than 6x6 inches, and if possible three or four
times as many plants should be raised as will ultimately
be required, in order that the best specimens may be
selected for planting.

The impossibility of selection is the chief objection
to the practice of planting seeds at stake, which is
sometimes adopted but is hardly to be recommended
on this account Another method widely employed in
the Federated Malay States consists in planting the
seeds in baskets, which are afterwards transferred to
the field bodily with the seedlings. To this method the
same objection will often apply owing to the insufficient
number of plants raised. Seedlings raised in baskets
can be planted out earlier than others, but the ad-
vantages of the method over that of stumping as
generally practised in Ceylon do not appear to be
conclusive, and it is decidedly more expensive.

In planting the nursery, the seeds should be carefully
laid in the ground in a horizontal position and just
covered over with soil. If the seeds are planted with
the long axis vertical, germination is less satisfactory
and some of the seedlings are likely to be contorted and

RUBBER PLANTING 101

twisted. The same area should not be used a second
time for a nursery unless it has been thoroughly dug
over with lime, in order to destroy any fungus and
insect pests which may have accumulated, and after-
wards allowed to lie fallow for some months. Thorough
fencing of the nursery is necessary in order to prevent
the depredations of larger animals.

Seed Selection.

In the early days of rubber planting, seed for nur-
series had to be taken where it could be got and
selection was out of the question ; but in the future
it ought to be possible to lay considerable stress on the
selection of seed. Among planters a marked predilec-
tion exists for the selection of seed from old trees.
Probably this preference rests upon some foundation
of fact, hence, other things being equal, seed should
be taken from old trees so long as these have not been
tapped too heavily. Much more important, however,
is the selection of seed from trees of known yield. We
have already had occasion to point out the marked
differences which exist between individual trees in the
matter of yield. It is of the utmost importance that
seed for future planting should be taken from the best
yielding trees. This is not such a simple matter as
might appear at first sight, on account of the scattering
of the ripe seeds which takes place when the fruits
burst. This phenomenon places a serious difficulty in

102 RUBBER AND

the way of the collection of seed from particular trees,
except on a very small scale. On estates therefore
which are going in for wide extensions and are in
possession of old trees already in bearing, the following
procedure may be recommended. A few acres should
be set apart definitely for seed bearing, as is done for
example in the case of tea. All the trees on this area
should be tapped in the same way for a definite period
— say for fifty tappings — and a record should be kept
of the yield of each individual tree. All except the
best yielding trees should then be ruthlessly cut down
and the stumps extracted in order to avoid the danger
of root disease. Tapping should then be stopped for
the whole period during which seed is required. In this
way not more than 20 per cent, of the original trees
should be left standing. If the distance of planting was
originally 15 x 20 feet this would leave about thirty
trees to the acre. With closer planting the selection
might be still more stringent. In felling, regard should
be had only to yield and not to size or position. Not
only would such a group of seed-bearers yield a return
from the sale of seed to neighbouring estates, but when
the demand for seed is over, tapping may be resumed,
and it is not impossible that the yield per acre from the
seed-bearers will be found to be as large as or larger
than that from any part of the estate not planted from
selected seed.

To those in charge of government plantations and
experiment stations a further course of selection may

RUBBER PLANTING 103

be recommended which is scarcely practicable on in-
dividual estates. This is the method of selection by
progeny which has been practised with great success
in the case of many annual crops. The method con-
sists in planting a number of definite areas, each of
an acre or less, with seed taken from the best yielding
individual trees selected over as wide an area as possible.
If practicable the seed of at least fifty trees should be
separately planted in this way. When the different
plots come into bearing their yields should be compared,
and a few of the best plots retained for seed bearing.
On the selected plots a comparison of individuals should
again be made by the only reliable test, namely indi-
vidual tapping, and the best yielding trees only should
be allowed to stand. The analogy of cinchona would
lead us to believe that if this method is carried far
enough a very marked increase in the average yield
of latex may be obtained. In Java the proportion of
alkaloid in the bark of the introduced cinchona plants
has been very nearly doubled by careful selection.
There is good evidence to show that the variation in
the yielding capacity of Hevea trees is considerably
greater than the normal variation in richness of cin-
chona bark.

Draining, Irrigation, Roads, etc.

Nurseries having been properly established, attention
may next be turned to the preparation of the fields for
planting. In the first place some kind of draining will

104 RUBBER AND

nearly always be necessary. In tropical agriculture
two totally distinct kinds of draining are to be dis-
tinguished. The first is the draining of swampy land
for the removal of superfluous water, and the second
is the cutting of transverse drains on sloping land, in
order to check the washing away of the soil, which
soon occurs when the original vegetation is cleared.

In the Federated Malay States rubber is frequently
planted on alluvial flats where the water level is only
a foot or two from the surface of the soil. In selecting
land for an estate in such a situation it is important
to remember that provision will have to be made for
carrying off the drainage water to a river or to the sea.
For this purpose canals of some size may have to be
specially constructed, and it may be necessary to acquire
the land occupied by the canal beyond the boundary of
the estate proper. The necessary canals are usually^ cut
by government before the sale of the land. In soil of
this kind numerous open drains are required, which may
be as much as three or four feet deep and two or three
feet wide. In some cases a drain is needed between
each row of trees, and the trees themselves are planted
on ridges formed by the materials thrown up in digging
the drains. In the Southern Province of Ceylon a
certain amount of rubber has been planted in swamps
similarly drained.

A large part of the rubber in Ceylon and other
countries is however planted on comparatively steep
hillsides, and here an entirely different system of

RUBBER PLANTING 105

drainage is required. Small drains about one and a
half feet in width and depth are carried across the
slopes with a fall of from I in 15 to i in 25. These
are made to discharge into any natural ravines or
watercourses which may occur. The distance between
the drains varies, according to the slope, from 100 feet
down to 20 feet or less. The earth removed in digging
is thrown out on the lower side of the drain. Loss of
soil may be further checked by interrupting the drains
with catch pits at frequent intervals. On very rocky
hillsides draining may be impracticable. In this case
some kind of terracing is frequently attempted by
building low walls of boulders below the trees. This
method is strongly to be recommended where drains
cannot be cut.

Irrigation has been little practised in the cultivation
of Hevea. In a dry climate the tree appears to suffer
more from the effects of sun and wind upon its young
branches and leaves than from lack of water in the soil.
Experiments in growing Hevea under irrigation in the
dry zone of Ceylon have so far been unsuccessful,
though it is possible that they might have fared better
if an effective wind-break could have been found.

The laying out of roads and paths leading to the
different sections of the estate is an operation which
should be undertaken at the same time as the tracing
of the drains, in order that the necessary culverts and
bridges may be provided for. Except in the case of
the principal tracks, little road-making is necessary

io6

RUBBER AND

beyond the provision of a drain on one or both sides
of the trace, and the building of suitable culverts or
paved watercourses to prevent breaching by floods.

Lining and Spacing.

The positions of the holes in which the trees will
be planted must next be marked out in lines at right
angles to a given base. It is important that these lines
should be laid out accurately in order to allow of an
uninterrupted view through the estate. If the first line
is laid out accurately, others can readily be placed by
simple measurement. A method of placing a line at
right angles to a base line is shown in the diagram. If
AC is made equal to BC and AD to BD the line CD
will be at right angles to the line AB.

Planting Distances.

The distance at which the trees should be spaced
is a matter which has given rise to much discussion.
The distances generally favoured in the Malay Peninsula

RUBBER PLANTING 107

give an average of about 150 trees to the acre, whilst
in Ceylon the average number is much nearer 200 to
the acre. Although different distances are suitable for
different soils and situations, it is generally agreed that
these numbers are too large for permanent plantations
and lead to excessive crowding by about the tenth year.
For future planting a distance of 15 x 15 feet may
probably be regarded as the absolute minimum, giving
nearly 200 trees to the acre without allowing for casualties.
Such a distance must ultimately lead to crowding. On
the other hand, a greater distance will almost certainly
entail reduced yields from a given area during the early
stages of tapping. Unfortunately there does not appear
to be any conclusive evidence yet published from which
a comparison can be drawn between the results of such
close planting and those of wider planting, as time goes
on. A consensus of opinion points to the greater value
of a smaller number of larger and less crowded trees ;
and it is at least probable that the crop will be obtained
more cheaply from such a plantation than from one
bearing a larger number of more crowded trees of the
same age. Twenty trees similar to the largest tree at
Henaratgoda — 35 years old — would yield upwards of
1000 Ibs. of rubber annually. 600 Ibs. per acre is about
the most that can be got from trees on similar soil
planted 12 x 12 feet at 25 years of age. The large tree
is however probably exceptional, whilst 12x12 feet is
certainly too close a distance. In the present state of
knowledge it may be thought that a suitable final

io8 RUBBER AND

distance is probably about 30 x 30 feet under average
conditions, or 50 trees to the acre.

Where a suitable inter-crop is available, an original
planting distance of 30 x 30 feet may probably be re-
commended. But where rubber is the only cultivation,
planting at such a distance means foregoing a con-
siderable amount of profit during the earlier stages.
It is therefore not likely that such wide planting will
often be adopted in practice. With closer planting
the question of thinning out will have to be faced later
on. This process will more properly be discussed at
a somewhat later stage.

The distances mentioned in the preceding para-
graphs apply to average conditions and may be
somewhat increased or reduced according to circum-
stances. It is convenient to remember that

TABLE XXVI

a distance of gives approximately actually trees

feet trees per acre per acre

12x12 300 302

15x15 200 194

15x20 150 145

20X20 100 IO9

30 x 30 50 48

35X35 35 35

The figures given above apply to planting on the
square. By adopting the hexagonal system of planting
the distance between any given tree and its nearest
neighbours is somewhat increased, keeping the same

RUBBER PLANTING 109

number of trees per acre. This is probably an ad-
vantage during the short period when the lateral
branches are just beginning to meet. The method is
somewhat more troublesome than the square system
and is seldom adopted. The arrangement of the trees
on the two systems is shown in Fig. 14.

xxx xxx

xxx x x x x

xxx xxx

Square system. Fig. 14. Hexagonal system.

Holing and Planting.

After the positions of the trees have been staked
out, holes must be dug for their reception. The holes
should not be less than one and a half feet each way,
and may conveniently be cubical. The larger the holes
the better will be the general growth of the plants.
They should be filled in with surface soil and allowed
to settle for some time before planting. The strongest
seedlings in the nurseries should be selected for planting
out, and all weakly and defective plants rejected. On
removal from the nursery the seedlings are frequently
stumped, that is to say the whole of the green top is
cut away, and the tap root is severed about 18 inches
below ground level, most of the lateral roots being also
cut short. Mr Tisdall tells me that it is a mistake to
cut the tap root and laterals too short. This operation,
which at first sight appears somewhat drastic, has great

no RUBBER AND

conveniences in practice and is not theoretically ob-
jectionable. If the leaves and smaller roots were left
upon the plants, both would be found to die back
except under remarkably favourable circumstances.
Stumps can be used which have grown for two and
even three years in the nursery, whereas it would be
impossible to transplant seedlings of that age with all
their roots and leaves. A good start for the plantation
is thus assured, and there should be few failures when
proper care is exercised. The earth should be rammed
tightly round the planted seedlings or stumps. For
early planting, seedlings grown in small loose baskets
may be used, as these can be set out earlier than plants
grown in the nursery in the ordinary way. The baskets
are planted with the seedlings and are allowed to rot
in the soil. When this method is adopted it is
specially necessary to make sure that weakly plants
are rejected.

Planting should of course be carried out in wet
weather, and in most countries where rubber is grown
this presents no difficulty. Should a prolonged drought
follow shortly after planting the young plants may
require some protection. This is often best afforded
by mulching with grass and leaves, or with anything
of the kind that may be available, close round the
plants, in order to check evaporation from the soil
surrounding the roots.

RUBBER PLANTING in

Rate of Growth.

In Ceylon under favourable conditions Hevea trees
will grow in height at the rate of 6 to 10 feet per annum
for the first three or four years after planting. In girth
the increase may be about 3 to 4 inches per annum
during the first few years. After this the rate may be
slightly increased until the lateral branches have com-
pletely met, and then growth becomes slower once
more. The greatest development takes place after the
third year. Some of the oldest trees in Ceylon, at
35 years of age, had a girth of over 100 inches, and
were about 80 feet in height. In Malaya the average
growth of young trees is still more rapid, and it has
been stated that the girth of four-year-old trees in the
Federated Malay States is generally equal to that of
five-year-old trees in Ceylon. The age of the trees is
always reckoned from the time of planting, and not from
the date of sowing the seed.

Weeding.

We next come to the vexed question of weeding.
It is the universal opinion of practical planters that
clean weeding from the burn off is cheapest in the long
run, and leads to better growth of the trees than any
other system. Cover plants should not be regarded as a
substitute for weeding. Leguminous plants if grown as
a source of nitrogen are to be regarded as a part of the

ii2 RUBBER AND

general cultivation and manuring of the estate. These
processes are additional to weeding and should not be
looked upon as an alternative. Weeding is almost
universally done by hand, but on suitable land the use
of agricultural machinery is strongly to be recom-
mended during the earlier stages of growth. The disc
harrow drawn by oxen is a most effective implement
for keeping down weeds and preserving a surface
mulch, whilst on large estates steam power might very
well be introduced. However, the presence of drains
or unevenness of the land renders the use of such
implements impossible on a large majority of rubber
estates.

In connection with weeds and the use of cover crops,
one remarkable fallacy, which has been again and again
repeated, requires to be very clearly pointed out. It has
been asserted that a close cover of leafy plants is a
preservative against the effects of drought ; and the
moist surface of the soil beneath such a crop has been
pointed out as evidence of the conservation of moisture.
It is perhaps difficult at first sight to realise that a dry
powdery surface is losing less moisture than a moist
surface, but a little thought will show that this is
certainly the case. The best preservative against the
effects of drought is a thick covering of dead leaves,
such as is actually present under old rubber when the
leaves have fallen, an event which occurs towards the
beginning of the dry season in Ceylon. Failing such a
mulch, the next best form of protection is afforded by

RUBBER PLANTING 113

keeping the surface of the soil loose and powdery, in
the form of what is known as a dust mulch, since a
caked surface evaporates much more water than a loose
surface. A leafy crop however is capable of evaporating
three or four times as much water as. a bare surface of
soil. In times of drought therefore a thick covering
of living weeds is a special danger, since the weeds
draw off the supplies of water available for the rubber
roots, and the crop is liable to suffer severely in
consequence.

On steep slopes a cover crop may be of distinct
utility in checking soil wash, especially if it is grown in
definite lines across the slope, and periodically cut down
and laid along the contours in order to form a series of
miniature terraces. For this purpose various species
of Crotalaria, Indigofera and Tephrosia may be used
with advantage, since these are leguminous plants which
also collect nitrogen from the air.

Intercrops.

If wide planting be adopted, some kind of intercrop
seems to be desirable in order that some revenue may
be obtained during the period before the rubber comes
into full bearing. In Ceylon, tea is commonly used for
this purpose, or more frequently the rubber is planted
at wide intervals through existing fields of tea. In this
case the growth of the rubber must be expected to be
slow. Rubber has also been planted somewhat widely
L. 8

ii4 RUBBER AND

through cacao, but this practice is objectionable owing
to the identity of several diseases to which the two
crops are subject, notably canker. Cotton has been
suggested, but the climates required by the two crops
are widely different, since a prolonged dry season is
necessary for the successful harvesting of the fibre. In
Sumatra and Java coffee is frequently grown in con-
junction with the early stages of rubber, and many other
crops have been suggested. Amongst these, Indigo is
one which seems to deserve more attention than it has
hitherto received. Indigo is an efficient gatherer of
nitrogen, and in the case of this crop practically the
whole of the materials removed from the soil, together
with the additional nitrogen, can be returned in the
so-called sect in a readily available form. Indigo
cultivation however requires special knowledge and
appliances, and these it might not be worth while to
introduce, owing to the comparative shortness of the
period available before the shade of the rubber prevents
the further growth of such a crop.

Schidrowitz and others consider that no intercrop
has yet been proposed which will give a return greater
than the relative loss occasioned by the slower growth
of the rubber, so long as the price of rubber remains
high. The question is not however finally settled, and
much depends upon whether it is decided to plant the
rubber trees at the distance at which they will finally
stand, or to adopt close planting and subsequent thinning
of the plantation.

Plate VI

RUBBER PLANTING 115

If the growing of an intercrop is decided upon, care
must be taken to allow plenty of space for the growth
of the rubber in its early stages. As the trees develop,
the shade of the rubber will generally bring the life of
the subsidiary crop to a close after it has served its
purpose. All traces of the latter must then be cleared
away, and no dead remains be left to serve as a centre
for the spread of fungus diseases.

Cultivation and Manuring.

Few data exist with regard to the effect of cultivation
on growth. Frequent deep forking has been tried on a
small scale in Ceylon, and has apparently no harmful
effect upon the trees. It is hardly to be expected that
this expensive operation can lead to much financial
profit when carried out over wide areas, although on
sloping ground an occasional forking has a marked
effect in checking wash. Mr Tisdall informs me that
cases of wonderful development in growth have occurred
as the result of annual deep forking in fields which were
thought unsuitable for Hevea, owing to the slowness
of growth during the early stages. Where the con-
ditions are favourable for the employment of agricultural
machinery, deep cultivation may profitably be employed
between the rows of rubber, in connection with the
eradication of weeds during the early stages of growth.
More often than not the use of such machinery will
be prevented by the frequency of drains, by the presence

8—2

n6 RUBBER AND

of rocks or other obstructions, or by excessive gradients.
Later on it is probably better to conserve the mulch of
fallen leaves and to imitate forest conditions as closely
as possible.

With regard to the use of manures, no really reliable
experimental work has yet been published, and opinions
can only be based on general principles and on
.plantation experience. The latter shows considerable
unanimity in favour of the use of artificial manures
on the poorer classes of soils. Such manures, especially
those containing nitrogen and potash, are said to exert
a markedly beneficial effect on growth, yield and renewal
during the earlier stages of the life of the tree. The
application of potash is said to be specially beneficial in
connection with renewal of bark. Phosphorus is found
in practice to have less influence on the functions
named ; and this is what would be expected on general
agricultural principles, since the use of phosphates is
generally closely associated with the formation of seed.
The application of phosphates may therefore perhaps be
suggested in connection with seed-bearers. Manures
containing potash have the advantage of being consider-
ably cheaper than nitrogenous and phosphatic manures.
An excess of nitrogen is to be avoided, as it is said to
make the trees top-heavy and brittle. Such an excess
is well known to lead to an extravagant production
of foliage in the majority of plants. Apart from this,
it does not seem likely that the application of artificials
in moderate quantities can have any deleterious effect

RUBBER PLANTING 117

upon a rubber plantation. The experience of the best
authorities in Ceylon shows that the annual application
of well chosen artificial manures leads to increased
growth and yield and to a better renewal of the bark
as well as to some immunity from disease.

Green Manuring.

Nitrogen is the most expensive of all the substances
required by growing plants. A sufficient supply of
nitrogen can most cheaply be added to soils, which
are deficient in this respect, by the practice of green
manuring. This method consists in growing some plant
which is capable of taking up nitrogen from the air.
The nitrogen is added to the soil by cutting down the
plants at the proper stage of growth and either
burying them or using them as a mulch. It is important
therefore that this process should only be undertaken
when there is plenty of labour available for dealing with
the green crop at the proper stage. The plants used for
green manuring belong to the natural order leguminosae.
They may conveniently be divided into (i) creepers and
climbers, (2) low growing bushy plants and (3) trees.

Creepers and climbers are not generally to be recom-
mended. They are difficult to deal with, are liable to
smother the young rubber trees if neglected, and form a
convenient cover for snakes and other vermin.

Among low growing bushy plants some of the best,
according to experiments carried out at Peradeniya, are

n8 RUBBER AND

Crotalaria striata^ Indigofera arrecta^ Tephrosia Candida
and Leucaena glauca. The last named plant grows into
a good sized shrub if permitted to do so, but it can be
kept coppiced and then provides a heavy mulch of
green shoots. Any of the above named plants may be
sown broadcast on level land or in transverse lines
on sloping ground. A maximum of green material is
generally available just before flowering, after four or
five months growth, when the plants have reached a
height of from four to six feet. The plants are then
cut down close to the ground and mulched round the
trees. On slopes they may be spread in the form of a
crescent some feet below each tree, in order to lead
to the formation of small natural terraces. Such a
mulch is specially valuable in times of drought, but
the method can only be applied with safety in countries
where the drought begins at stated periods. The cutting
and mulching must be carried out at the beginning of
such a period, otherwise the green crop will dry up
the soil by evaporating water. The dry stems left after
cutting lead to no appreciable loss of water, whilst the
green mulch is a valuable protection. After cutting,
the plants throw up fresh shoots, and in a moist
climate they can be cut repeatedly at intervals of four
or five months. Ultimately their growth is checked
by the shade of the rubber and they should then be
uprooted.

In situations where it will grow freely, one of the
best types of tree for green manuring is the dadap,

RUBBER PLANTING 119

Erythrina lithosperma. This may be planted alternately
in the rows of rubber, and can be conveniently raised
from cuttings after a stock has been obtained from seed.
The best cuttings are stout branches five or six feet
long and three or four inches in diameter. These are
planted like so many posts, and develop into good
sized trees in little more than a year. Care must there-
fore be taken that their growth is not allowed to interfere
with that of the rubber. The green branches are
pollarded at suitable intervals and mulched as already
described in the case of smaller plants. The shelter
afforded by the dadaps is often valuable while the
rubber is young, and their presence tends to draw up
the latter into tall saplings and to check branching
close to the ground.

Shade and Wind Belts.

Rubber requires no permanent shade, and indeed few
trees would be tall enough to afford it. The protection
of dadaps, as already described, is often valuable in the
early stages of growth, and this is specially the case in
wind-swept situations. The interplanted dadaps afford
an excellent protection from the wind, but they should
not be allowed to top the rubber for too long a period.
Dadaps or similar trees may also be grown con-
veniently in belts across the direction of the prevailing
winds in cases where interplanting is considered
undesirable. They may also be introduced where a

120 RUBBER AND

low growing intercrop has been planted which affords
no protection.

Pruning.

Except for the removal of dead branches, pruning is
not generally recommended in the case of well grown
rubber trees. Weak drooping branches which prevent
the access of sunlight to the tapping area may, however,
often be removed with advantage. Formerly a process
known as thumb-nail pruning was advocated, in which
the terminal bud of the tree was nipped off when a
height of 12 to 15 feet had been reached. The result of
this treatment was to cause a forking of the tree into
two or three main branches, and it was claimed that
the rate of increase of the girth of the main trunk was
thus accelerated. The objection to the method lies in
the fact that the fork becomes a point of weakness, and
the tree becomes very liable to split at this point if
at all exposed to wind. Such a fork also forms a
convenient point of lodgement for fungus spores, and
may thus lead to the origin of disease. The method is
specially to be avoided in countries where Pink disease
is prevalent. One form of pruning is, however, often
necessary in the case of young trees, especially when
widely planted. Any lateral branches which occur below
a height of about ten feet should be cut off flush with
the stem as early as possible, in order that the future
tapping area may not be obstructed.

RUBBER PLANTING 121

Thinning out.

There can be no doubt that thinning out is a problem
which will soon have to be faced on the majority of
estates, and on many the process is already in operation.
The most important principle to be observed in thinning
/is to disregard the position of the trees. In the opinion
of the writer, it would be a great mistake simply to
remove alternate trees regardless of their individual
value. Under ordinary conditions, whatever the position
of the remaining trees may be, and however large the
gaps caused by felling, the roots will soon explore the
whole of the remaining soil, and the branches will come
after a time to occupy the remaining air space. In
the first place then, all weakly or diseased trees should
be removed, and secondly all those which are found
to give the poorest yields of rubber. Large trees may
have to be taken down in sections, since their fall would
lead to injury of the surrounding trees. The stumps
must next be dug out or extracted. The site of the old
tree should be thoroughly dug over and well limed,
and as much of the roots as possible taken away. All
dead wood and roots must be burned. The older parts
of Hevea make a fairly good fuel which may be utilized
in the factory.

Oil from Rubber Seeds.

It has been suggested that the collection of the seeds
which are now produced in large quantities on Hevea
plantations may form the basis of a profitable minor

122 RUBBER AND

industry, since the kernels contain about 40 per cent,
of an oil which is similar to linseed oil, and has been
favourably reported upon by chemists at home. The
suggestion to lease out the right of collecting the seeds
does not appear a very happy one, owing to the
opportunities for thefts of rubber which such an arrange-
ment would afford. But at times of abundance the
collection could be readily carried out on the estate by
children too small to take part in the tapping and other
regular work.

Hevea seeds weigh about 7 Ib. per thousand, and
the cost of collection last year was given by the
Superintendent of the Peradeniya Experiment Station
as under half a cent a pound. As the kernels represent
approximately half the weight of the seeds, a ton of
kernels will not cost more than Rs. 22.50 to collect
under these circumstances. To this must be added the
cost of decorticating the seeds, and for this purpose
machines are under trial, with which it is hoped to per-
form the operation at a comparatively small expense.
It is possible that the development of this subsidiary
industry will form an appreciable addition to the value
of rubber estates in the future.

Labour.

In densely inhabited countries like Java and South
India, where the native population is obliged to work
hard in order to obtain a meagre living, efficient labourers

RUBBER PLANTING 123

for employment on plantations are readily available at
low wages. These two countries also provide a large
number of emigrants to other parts of the Eastern
Tropics which are less favoured in this respect, owing
to the indolence or small numbers of the native popula-
tion. Even in India a good deal depends upon the
position and healthiness of the plantation. In every
country some estates are always well supplied with
labour, whilst others are exposed to constant difficulties
in this respect.

Ceylon has also a considerable native population,
and the number of Sinhalese labourers on rubber estates
is increasing. The supply is however by no means
equal to the demand, and the deficit is made up
exclusively by immigrant Tamils and kindred races
from the neighbouring peninsula. In Sumatra the
labour employed on the rubber estates is principally
immigrant Javanese, emigration being permitted by the
Government of the Dutch colonies subject to certain
regulations. The Malay Peninsula is comparatively
thinly populated, and the Malays do not take kindly to
regular work on plantations. There is also a consider-
able Chinese population, of which many are employed
in the mining industry ; but Chinese labour has not
been found entirely satisfactory for harvesting rubber,
although the Chinese are widely employed in clearing
and planting. In addition to a certain number of
Chinese, Javanese and Malays, the rubber estates are
principally supplied with indentured labour from

i24 RUBBER AND

Southern India. Indeed, the drain of coolies from
favoured districts in South India has recently been so
great that the local planters are finding a difficulty in
supplying their own needs, and there is a tendency to
place obstacles in the way of further emigration. Large
areas still exist, however, which have not yet been
exploited by the labour agencies, and a good deal can
probably still be done in this direction.

The number of labourers employed on estates of all
kinds in the Federated Malay States in 1910 was
approximately as follows : —

TABLE XXVII
Labourers on Rubber Estates in Malaya in 1910.

Tamils 99,000

Chinese 46,000

Javanese 18,000

Malays 14,000

Others 2,000

Total 179,000

The great majority of the above were at work on rubber
estates.

The number of Indian Tamils in Ceylon is probably
nearly half a million, of whom perhaps a quarter are
employed in the rubber planting industry. Every year
a considerable proportion of these labourers returns to
India by way of Tuticorin. The Manaar Railway is
expected to be open next year, when the Tuticorin route
will be little used. This increased facility will probably
increase the flow of immigration.

RUBBER PLANTING 125

Where recourse is had to immigrant coolies, the cost
of their introduction must be paid by the estate, and in
addition some advance is usually made, which may or
may not be wholly recoverable from the labourers'
wages within a certain number of years. In recent
years, owing to the competition for labour, the system
of advances in Ceylon has given rise to much abuse,
and a state of affairs has arisen which is entirely
opposed to the best interests of employer and employed
alike.

The rates of wages paid to immigrant coolies,
although sufficient to attract large numbers to leave
their native country, are not very high according to
western ideas. A good worker on a Ceylon rubber
estate may earn from 50 to 60 cents a day (&£ to lod.)
and in the Malay States rather more. The governments
of these countries have recently introduced legislation
to protect the interests and welfare of the labourers, and
increased attention is paid to their comforts and sanita-
tion, whilst hospitals and schools are now being provided
in all districts.

Other Expenses.

In addition to the work already described, some of
the other items of expenditure involved in opening up
an estate may here be briefly enumerated. In the first
place, there are the salaries of the Superintendent and
his assistants, and the wages of native overseers,
watchers and guards. Houses must be provided for

126 RUBBER AND

all these in addition to " lines " for the coolies, stores,
hospital and dispensary, cart sheds and other buildings.
On large estates horses and stabling must be provided
for the Superintendent.

A full survey of the estate is necessary, and a large
scale map should be prepared showing watercourses and
other physical features, together with the subdivision of
the estate into fields of 50 or 100 acres. Carts or lorries
or boats will be required, according to the method of
transport adopted. The food of the coolies is mainly
supplied by the estate and charged to their account.
Other items are medicines, cattle food, fuel, etc.

Tools.

The large hoe universally employed for digging in
the barefooted East is known as a chankol in Malaya
and as a mamoti in Ceylon. Digging, draining and a
certain amount of weeding are done with this imple-
ment. Felling axes, cross-cut saws and bill hooks are
required for clearing, and for lighter work the parang is
used in Malaya and the katty in Ceylon. For nursery
work, rakes and watering cans are required, and a kind
of crow-bar is generally used for digging holes for
planting. These, with priming knives and saws, com-
plete the list of tools required on a rubber estate before
the time for tapping arrives.

In addition to the above, the Superintendent will
require measuring tapes and chains and a few simple
surveying instruments.

RUBBER PLANTING

127

I am indebted to Mr W. N. Tisdall for the following
estimate for planting 500 acres of rubber and for bringing
it into bearing under average conditions in Ceylon :

Purchase price of Crown Land may be any figure
between Rs. 75 and 250.

First Year (opening).

Felling and clearing

Holing 2o'x2o', 1 08 @ 6 cts

Filling

Liming

Weeding, 6 months @ 2/-, 6 months @ 1/50

Planting

Nurseries and plants

Fencing (Barbed and Mesh)

Roading, including blasting, etc

Draining „ „

Supervision ...

Buildings, 50 coolie rooms ©25/2

Bungalows, etc.

Coolies, advances, 200 @ 6o/-

Medical, etc.

Second Year.
General upkeep and supplying, etc.

Third Year.
General upkeep and supplying, etc.

Fourth Year.
General upkeep and supplying, etc.

Fifth Year.

General upkeep and supplying, etc.
Permanent Buildings, etc.

Per acre

15.00

6.48

i.oo

1.50

21.00
1.50
5.00

10.00

12.50

17.50
15.00

2.50
3.00

20.00

5.00

50.00

45.00

40.00

35.00

120.00

Rs. 426.98

The sixth year should show a good return. Under
favourable circumstances this estimate could be reduced,
but it provides for the best class of work.

CHAPTER VI

HARVESTING OPERATIONS

Introductory.

PREPARATIONS for tapping the trees are generally
begun when the plantation has reached an age of four
or five years from planting. In each field over a certain
age — usually not less than four and a half years — the
trees are measured and numbered. All trees over a
certain girth — usually not less than 18 inches at three
feet from the ground — are then marked out for tapping
on one or other of the systems presently to be described.
The age at which the trees can first be tapped is largely
determined by the thickness of the available bark.
Experience has shown that trees of 18 inches girth and
upwards can generally be lightly tapped without injury.
This size, as we have seen, corresponds to an age of
from four to six years. At this age the bark has
reached a thickness which is capable of sustaining the
effects of careful tapping and of making a satisfactory
renewal, whilst yielding a certain amount of latex.
From trees of a smaller size than this the yield hardly

RUBBER AND RUBBER PLANTING 129

repays the cost of tapping, and the risk of serious
injury is great owing to the thinness of the bark. If
the planter can afford to wait until the trees have
reached a somewhat larger girth so much the better.

Before describing methods of tapping in detail, we
may give a general account of the ordinary routine of
an estate on which the harvesting of the rubber is in
progress. A start is made in the very early morning,
since the earlier the trees are tapped the more freely
does the latex flow. Each tapper has a certain number
of trees assigned to him or her. In some cases each
worker is allotted the task of tapping a certain number
of trees and is paid by the day. On other estates
payment is made according to the quantity of rubber
obtained. In such cases each tapper has the run of
a somewhat larger area. In either case the quality
of the work performed requires thorough supervision,
since the least carelessness in tapping may lead to
serious injury of the bark. At the first round the trees
are tapped and collecting cups of tin, glass or coconut-
shell are placed in position to receive the latex. When
the tapping round is completed, the coolie makes a
second round provided with a pail of enamelled iron,
into which the contents of the several cups are poured.
The latex is carried to the factory, where the quantity
obtained by each tapper or group of tappers may be
separately coagulated, and the wet rubber weighed,
before it passes on into the general stock. A third
round may then be made in order to scour the cups and
L. 9

130 RUBBER AND

to collect the scrap rubber which has congealed in the
cups or upon the bark of the tree. More often this
work is relegated to a less experienced hand. Periodi-
cally also the shavings of bark which have fallen upon
the ground are collected, and even the earth upon
which latex may have trickled is not wasted; from
both these sources low grades of rubber are extracted
in the factory.

Tapping processes may be divided into methods of
incision and methods of excision. In the excision or
paring methods, which are almost universally employed
in practice on estates, a thin shaving of bark is removed
from the tree at each tapping. Incision methods are
designed to extract the latex by pricking or gashing
without removal of bark.

Incision Methods of Tapping.

Methods of incision or pricking have many points
to recommend them, at least in theory. If we are to
credit the dictum of Mr Herbert Wright, that the best
method of tapping is the one which leads to the greatest
flow of latex with the least possible removal of bark,
a pricking system in which no bark is removed should
be superior to any method of paring. There are
however many other points to be taken into considera-
tion besides the flow of latex and the removal of the
bark. It may therefore prove instructive to discuss the
disadvantages under which some systems of pricking

RUBBER PLANTING 131

labour as compared with good paring. From such a
discussion we may hope to arrive at an understanding
of the features which should characterise an ideal system
of pricking.

The method of incision was employed by Trimen
in Ceylon prior to 1888, but the precise method adopted
was not exactly specified. Among the earliest methods
of incision practised upon planted trees, of which we
have a satisfactory record, was the one employed by
Parkin in experiments at Henaratgoda. Parkin's
method, which was based on those used in the col-
lection of wild rubber in Brazil, was to make V-shaped
cuts in the bark by the aid of a hammer and chisel.
With this method two definite defects are associated
in practice. A separate collecting cup is required for
each V, whilst the surface of the tree becomes rough
and lumpy owing to the irregular renewal thus induced,
until further tapping becomes a difficult matter. More-
over, except in the case of old trees with very thick bark,
it is impossible to avoid more or less extensive injury
to the cambium. The method is quite unsuitable for
young trees.

The fact is that no method of large incisions truly
conforms to Wright's definition of good tapping, since
such incisions entail the destruction, if not the removal,
of a considerable mass of living cortex. This destruc-
tion goes much deeper than that caused by careful
paring, and often involves the cambium itself. On the
other hand, a small clean prick, such as may be made

9—2

132 RUBBER AND

with the point of a pen-knife, generally heals up com-
pletely without any sloughing off of cortical tissue, in
spite of the fact that the blade has actually penetrated
to the cambium. Such a prick also leads to a con-
siderable flow of latex in comparison with the size of
the wound inflicted.

The time required for making small pricks singly
is clearly prohibitive of their use as a practical method.
For the rapid infliction of a large number of pricks the
rotating spur-shaped pricker was introduced by Bowman
and Northway in 1905, and has enjoyed a considerable
vogue in Ceylon. A single stroke from one of these
tools produces a row of pricks running across the bark
of the tree. Owing to the difficulty of collecting the
latex thus liberated by any other method, the use of
the spur-shaped pricker was generally combined with
a shallow system of paring. The pricker was run
along the paring cut either on the same day or on the
day following, and the cut provided a channel down
which the latex could flow. The great theoretical
objection to this method lay in the closeness of the
pricks inflicted on successive days. Although the bark
of a healthy tree generally recovered from the operation,
there was a considerable sloughing off of cellular tissue.
Moreover, in the freshly pricked region the blockage of
phloem tubes necessarily produced must have amounted
to partial ringing of the tree. It seems clear too, that
in some cases the use of this method was associated
with an epidemic of woody nodules (see Chapter vill).

Plate VII

Photo C. Xortlnvay

Hevea Tree pricked with Serrated Knife

RUBBER PLANTING 133

Finally, there is clear evidence that a better yield,
without any greater loss of bark, is obtained in the long
run by simple paring than by combined paring and
pricking.

Pricking Methods under Trial.

A method has been developed on an estate in the
Southern Province of Ceylon which seems to avoid
many of the drawbacks hitherto described. The trees
are tapped on a herring-bone system, and each rib of
the herring-bone is simply represented by four small
pricks made by a single insertion of a " serrated knife."
This pricker has square teeth a quarter of an inch wide,
with a similar interval between each tooth. They are
thus practically identical with what is known as Mac-
adam's comb pricker, except that the number of teeth
is only four. A shallow conducting channel is cut
vertically in the bark of the tree, and with a little
assistance from the tapper the latex flows into the
channel and down the tree. The original incisions,
covering an area 2 inches in breadth, are made at
vertical' intervals of a foot, and on each day following
a similar set of incisions is made at ^ to f inch below
the old ones. When the first area is completed after
24 days' tapping, the whole operation is repeated on the
opposite side of the tree. Subsequently similar figures
are intercalated between the old ones until only one
or two narrow strips of bark are left untapped. A
return is then made to the original area after a period

134 RUBBER AND

of rest, which is more or less extended according to the
freedom with which the latex is found to flow.

The method here described is open to the same
abuse as all other pricking systems, in the temptation
which it presents of overtapping small trees. But if
no trees under 18 inches in circumference are tapped,
and if the method is adopted of resting any field which
shows a falling off in yield, the system seems to be
largely free from theoretical disadvantages. According
to Mr Tisdall, a noticeable feature in this method of
pricking is the immunity of the tree from canker and
bark-rot in comparison with the paring system, and the
healthy appearance of the foliage after an extended
period of tapping. So far the disadvantages appear
to be the difficulty of collection in wet weather and the
extra cost of tapping as compared to paring. On the
estate where the system has been evolved, highly
satisfactory yields are said to be obtained by this
method. The system may be recommended for trial
elsewhere, bearing in mind that a method of tapping
which suits one district is often quite unsuccessful in
another.

Another incision system, suggested by Mr Kelway
Bamber, has been on trial for some time by the Botanic
Department of Ceylon. The method is deserving of
mention on account of the large yields which have
been obtained from young trees without apparent
damage.

Bamber's method consists in cutting two vertical

RUBBER PLANTING 135

channels on opposite sides of the tree, and pricking
down these from top to bottom with transverse cuts
an inch apart. The cuts are made with a thin blade
about three-quarters of an inch wide and rounded at
the end. On alternate days two similar channels are
cut an inch to the right of the former ones and pricked
in the same manner. When the whole of the circum-
ference has been tapped in this way, the tree is rested
until the beginning of the second month from the
commencement of tapping, and the process is then
repeated, the same vertical channels being cut smooth
and re-pricked. In this way the larger trees are tapped
more frequently than the smaller ones. On a particular
acre bearing 147 trees the average number of tappings
was 75 in a year. The trees were just five years old
at the commencement of tapping, and ranged in cir-
cumference from 10 to 21 inches. All the trees were
tapped without exception, and the average yield for
twelve months was 18 ounces per tree, or 164 Ibs. per
acre. This is a remarkably high yield for 5 — 6-year-old
trees at an elevation of 1500 feet in Ceylon. At the
end of the year only a few of the smallest trees appeared
to have suffered any harm from the process.

v'fhe chief objections to this system are the large
amount of labour required, and the large proportion
of the rubber which is obtained in the form of scrap,
namely, nearly 50 per cent, of the total quantity. It
is however a method which may well be adopted in
tapping trees which it is ultimately intended to thin out

136 RUBBER AND

on closely planted estates. How far it can be adopted
as a permanent system of tapping can only be deter-
mined by further trial.

Excision Methods of Tapping.

At the present time the method which is almost
universally adopted on estates is paring on some system
or other. The results are generally so satisfactory that
paring is not likely to be given up in favour of any
method of pricking, until very clear proof of the
superiority of the latter is forthcoming.

The precise system of paring will partly depend
upon the period which is to be allowed for bark re-
newal. At the present time it is generally recommended
that the renewed bark should not be touched until a
period of four years has elapsed from the beginning
of tapping. There is some reason for believing that
even this interval, which is longer than that formerly
adopted on many estates, may be profitably increased.
It is probable also that a longer period is required for
each successive renewal.

As regards the size of tree upon which paring may
safely be begun, it is generally considered that trees
less than five years old from planting should not be
tapped at any point where they are less than 18
inches in girth. The reason for this restriction is that
where the circumference is smaller, the bark is so thin
that it is almost impossible to pare without causing

RUBBER PLANTING 137

injury to the tree. Some authorities would increase
the minimum size allowed to a girth of 20 inches or
more.

If it is decided to allow four years for the renewal
of the bark, the simplest system which can be adopted
is to divide the circumference of the tree into four equal
parts, and to tap these successively by the half-herring-
bone method. Each quarter section of the tree will
then represent a year's tapping. The quarter section
opposite the first should be tapped second, and then the
other two sections successively, in order to preserve the
symmetry of the tree as far as possible.

Systems of Paring.

The system of tapping adopted in the experiments
described in Chapter IV was one of superimposed Vs.
The cuts were made at an angle of 45 degrees with the
horizon, and the vertical distance between successive
cuts was one foot. In describing other systems we may
assume for the present a similar angle of cut, and a
similar distance between successive cuts where there are
more than one. The half-herring-bone system (Fig. 16)
referred to in the last paragraph consists of a vertical
conducting channel into which a single series of slanting
cuts leads on one side only. Such a system may be
derived from the superimposed V system by obliterating
one limb of each V. Reasons have already been given
for confining such a system to one quarter of the

138 RUBBER AND

\ \ \ \ \

\ \ \ \ \

RUBBER PLANTING 139

circumference. A similar system, extending over half
the circumference of the tree, has however been widely
used on estates, and is known as the half spiral system
(Fig. 17). The full spiral system was once popular
but is now almost obsolete, as it proved too drastic.
In this system one or more similar cuts extended right
round the tree, or even girdled it more than once. There
was no vertical channel, but each spiral cut drained into
a separate collecting cup. In the full herring-bone
system (Fig. 15) there is a conducting channel with
slanting cuts on either side. The lateral cuts enter the
central channel alternately instead of meeting as in the
V system. The herring-bone method is generally pre-
ferred to the V system because in the latter the bark
at the tips of the V's is said to be specially liable to
injury. The full herring-bone system is often used on
large trees, on which the lateral cuts would have to be
of considerable length if the half-herring-bone system
were employed. To mention only one other system —
on young trees in Malaya a single basal V (Fig. 19) is
often tapped. By this method trees can be tapped
close to the ground, although the bark at a higher level
is not yet ready for tapping. The basal system is also
being used on older trees on some estates, and it is said
that the yield is almost as good as when two or three
cuts are employed, whilst there is of course a great
saving of bark.

140 RUBBER AND

Marking the Tree.

When the age for beginning tapping has been
reached, all the trees on a particular field are generally
numbered consecutively. The trees are measured, and
those which exceed a certain girth are marked out for
tapping. It may be useful to describe a method of
marking in some detail, in order that the system
adopted may be clearly understood. The method of
tapping to be described is the half-herring-bone on a
quarter of the tree.

We will suppose a tree to be 20 inches in girth at
4 feet 6 inches from the ground. At this level a hori-
zontal line is stencilled round the tree. From two
points 5 inches apart on this line two vertical lines AB,
CD are ruled down to the foot of the tree by the help
of a straight edge. The tree may be perhaps 24 inches
in girth a foot from the ground. If so the lines will
be 6 inches apart at the point 5. These lines should be
so arranged that the equidistant points B, D, F, and H
fall between the main lateral roots of the tree, which
generally project above the level of the ground ; other-
wise there may be a difficulty in getting the collecting
cups to stand upright, when tapping is in progress.

Next a mark is made at P, 5 inches below A, so
that AP is equal to AC. A line drawn from P to C
will then make an angle of 45 degrees with the hori-
zontal. Marks Q, Ry S, T, [7, and V are made at
intervals of a foot below P and C respectively, and lines

RUBBER PLANTING

141

are drawn joining up PC, QT, RU> and SV. These
lines represent the positions of the original tapping
cuts. The lower lines will make angles of rather less
than 45 degrees with the horizon, but the slope will not
be so much less as to make any serious difference in the
result of tapping.

G A C E G

H

D
Fig. 20.

H

This method of marking will be found more ac-
curate than that of measuring up from the ground, since
the ground level on different sides of the tree is liable

H2 RUBBER AND

to vary considerably. The lines are best marked boldly
with a tapping knife, in order to leave a permanent
trace on the surface of the trunk.

From P nearly to B a broad shallow groove is cut
with the tapping knife in order to form the conducting
channel for the latex. The line CD should also be
marked out with a clear cut, in order that the tapper
may keep within the limits of the area allotted to him.
It will further conduce to accurate work if additional
guide lines are stencilled between the original tapping
cuts, and parallel to these, at intervals of about 3 inches,
as shown within the area QTUR.

In the above example the original tapping cuts
have been placed 12 inches apart,, in order to allow of
a year's tapping on alternate days at the rate of 1 5 cuts
to the inch — 180 cuts in all. It is reported that in
many parts of the Malay Peninsula the average width
of the daily shaving removed is considerably less than
one-fifteenth of an inch. When this is the case the
original cuts may be placed somewhat closer together.
On the other hand, if daily tapping be adopted it
may be necessary to place the original cuts further
apart.

In the case of smaller trees — those which are less
than 20 inches in circumference at a foot from the
ground — tapping may be begun on a single basal V,
as shown at XYZ in Fig. 20. After this V has been
tapped for a year, the tree will probably be large
enough to allow of placing two or more half-herring-

RUBBER PLANTING 143

bone traces on the opposite side of the tree. In this
case the areas A CBD and A GHB would next be tapped
in succession, followed by a further half-herring-bone on
the area CX VE above one-half of the original V.

The Paring Process.

The actual process of tapping is as follows. The
opening cuts are narrow grooves cut in the outer bark
and extending to within about one-eighth of an inch
of the cambium. It is important that the depth of
the groove should be exactly the same throughout its
length. The distance from the cambium can be gauged
by pricking with the blade of a pen-knife. Further
tapping consists in removing a thin shaving from the
lower side of the original groove on each occasion, always
to exactly the same depth. Coolies soon become very
expert at this work, but constant supervision is neces-
sary in order that no damage may be done. If the
tapper makes a mistake and cuts too deeply, injuring
the cambium, he should' be instructed to make three
or four very shallow cuts immediately below the wound,
so as to leave a thick piece of bark from which healing
can take place. If tapping is continued to the normal
depth — no matter how carefully it is conducted — the
wound is almost certain to spread. In the best tapping
the cuts are made to slope slightly inwards in order to
form a suitable groove by which the latex can reach
the conducting channel. The latex may need a little

144

RUBBER AND

encouragement before it will flow smoothly in the right
direction, without overflowing the channel. The merits
of good tapping consist in taking off the thinnest
possible shavings compatible with a free flow of latex
and preserving an even depth of cut, close to the
cambium but never touching it. The cuts should be
as clean and as sharp as possible.

Tapping Tools.

Of tools used in paring there is a great variety upon
the market. Many of these are highly effective, and it
is not our business here to puff the goods of any
particular maker. The writer's view is that the simplest
tools are the best, and that a great deal is to be said for
the original and primitive forms — the gouge and farrier's
knife — or slight modifications of these. Such tools are

Fig. 21. Gouge and Farrier's knife.

very widely used in the Malayan plantations, but the
Ceylon planter seems generally to prefer a more compli-
cated weapon. The simpler tools may necessitate
greater care at first on the part of the tapper, but

RUBBER PLANTING 145

once the requisite skill is attained, the greater
adaptability of the simpler tool and the greater ease
with which it can be kept sharp, enable the worker
to preserve a very straight line and to remove a very
thin shaving, keeping at the same time an accurate
depth of cut.

Angle of Cut.

The fact that an angle of 45 degrees with the
horizon is often adopted for the lateral cuts is largely
a matter of convention. A more acute angle than
45 degrees is seldom used, but flatter cuts are adopted
on a good many estates. Careful and prolonged experi-
ments are required before any definite statement can
be made as to what is the best angle under various
circumstances and with different systems of tapping. A
flatter cut opens the same number of latex vessels as a
more acute cut extending over the same horizontal
distance, and consequently releases an equal amount of
latex with the removal of less bark. On the other hand,
the latex flows more freely along a steeper cut, and
a smaller proportion of scrap is thus obtained. When
the consistency of the latex is moderately thin, the
angle of the cut can probably be reduced to one of
about 30 degrees without any loss of flow and with some
slight saving of bark.

10

H6 RUBBER AND

Direction of Cut.

In the half-herring-bone and half-spiral methods of
tapping, the cuts are usually made from the right to left
of the operator. There is a considerable body of
evidence to show that more latex is obtained in this
way than from cuts made in the reverse direction. The
reason for this phenomenon is not entirely clear. It
may partly be associated with the fact that tapping
from right to left is easier for a right-handed person,
and is therefore carried out more efficiently. But this
does not seem sufficient to account for the whole of the
difference.

Distance Between Successive Cuts and Yield
at Different Levels.

In various systems of tapping, a distance of one foot
between successive cuts has been very widely adopted.
Here, again, prolonged and laborious experiments are
required in order to ascertain what is the most profitable
distance to adopt in the case of each system and under
various conditions. The evidence contained in the
following paragraphs, which bears partly on this ques-
tion, requires to be greatly elaborated.

When a fairly old tree is first tapped by a herring-
bone or multiple V system, adopting the usual interval
of a foot between the cuts, it is found that the latex
flows in nearly equal quantity from each cut of the
vertical series. As the bark between the several cuts
becomes used up, a relatively larger proportion of latex

RUBBER PLANTING 147

is found to flow from the lowest cut; and some of the
upper cuts may even cease altogether to yield latex,
whilst there is still an inch or more of bark remaining
untapped. It is probably best in all cases to leave the
last inch or so of bark untapped, and to continue tapping
the lowest cut only, if the time has not arrived for
passing on to a fresh area of bark. When the same
section of the tree comes to be tapped a second time, it
may be marked out an inch higher than before, in order
that the unused slips of bark may now be tapped first.

In an experiment at Henaratgoda 29 old trees were
tapped daily on six wide NTs, spaced at vertical intervals
of a foot. During the first month's tapping the three
upper cuts yielded together a daily average of 558 c.c.
of latex (nearly a pint), and the three lower cuts a daily
average of 561 c.c. The quantities were therefore almost
exactly equal, although the latex from the lower cuts
contained a slightly higher proportion of rubber.
During the six months' tapping, at the end of which
the bark between the cuts had been almost entirely
removed, the average daily yield from each of the six
cuts was as follows:

TABLE XXVIII

Cut 12345 6

Yield c.c. ... 77 86 98 82 83 400

Thus, when the bark between the cuts was nearly
exhausted, the lowest cut was yielding as much latex as
all the other five put together. In addition, the latex

TO — 2

i48 RUBBER AND

from the lowest cut was more concentrated and con-
tained a higher percentage of rubber.

The trees described above were old, and possessed a
good thickness of bark. In the case of younger trees
we should probably expect the difference to be still
greater. On the other hand, the rate of tapping was
exceedingly rapid, the whole of the bark being removed
from one side of the tree in six months. The evidence
on the whole, however, seems to point to the conclusion
that the distance between successive cuts may profitably
be made greater than 12 inches. In other words, a
reduction in the number of cuts on a given area of bark,
as compared with the systems now generally adopted,
would probably lead to more satisfactory results.

The above experiment shows further that in the case
of mature trees there is little difference between the
initial yields of latex from areas of bark situated at a
height of I — 3 feet and 4 — 6 feet from the ground
respectively. Generally speaking, there is a slight
falling off in yield as we pass up the trunk from ground
level, owing to the diminished thickness of bark and the
smaller girth of the tree. In the lower part of the
trunk of mature trees this falling off is not very rapid,
and the fact that tapping is often confined to the lowest
six feet of the trunk is largely a matter of convenience.

It must be remembered that the lowest cut of all
drains a larger area of bark than any of the other cuts,
a fact which partly accounts for the very much larger
yield obtained from it.

RUBBER PLANTING 149

Tapping Intervals.

The effect of different intervals between successive
tappings on old trees has been discussed at some length
in Chapter IV. So long as the yield from a young
plantation continues to increase steadily, we have not at
present sufficient grounds for recommending any change
from the interval of one or two days which is usually
adopted ; in fact there is evidence that in the case of
young trees the yield per tapping may decrease as the
interval between successive tappings is extended. In
the case of older plantations of closely planted trees, if
the yield shows a tendency to remain stationary or
to fall off, we would suggest the trial of twice as long
an interval without any other alteration of the system in
use. We should not be greatly surprised if the planter
were to find after some months that he is harvesting
as much rubber as before, with an expenditure of only
half the labour.

Difficulties and Precautions.

The physiology of latex production was discussed in
Chapters in and IV as fully as is justified by our
limited knowledge of the subject. The present section
contains a few general remarks in relation to tapping.
One of the chief troubles of the latex collector consists
in the washing away of the latex which occurs in
wet weather, owing to the rain water which streams

i5o RUBBER AND

down the trunk of the tree. Rainy days generally make
up a large proportion of the tapping season, and if
tapping is stopped whenever there is heavy rain, the
loss of yield will be considerable. A simple system of
guttering has recently been introduced in Ceylon, which
can be fitted to the tree above the tapping area, with the
object of keeping the latter dry.

Another reason for keeping dry the tapping area,
lies in the fact that this region is more susceptible than
any other to the attacks of disease germs. A constant
watch should therefore be kept on the tapping cuts,
and at the first sign of disease tapping should be
suspended. There are two reasons for ceasing to tap
a diseased tree ; firstly in order to allow the individual
tree to recuperate, and secondly to avoid the trans-
ference of infection to other trees by means of the
tapping knife.

In the absence of visible signs of disease, certain
cuts are sometimes found to yield little or no latex,
whilst there is still a comparatively free flow from other
cuts. When this is the case, the hint should be taken
and the tree rested, otherwise definite disease is not
unlikely to supervene. For a description of particular
diseases and their treatment, reference may be made to
Chapter VIII.

At the bottom of the conducting channel a tin spout
should be fixed into the bark, in order to throw the
latex clear of the surface of the tree into a cup placed
on the ground below. The practice of pushing the

RUBBER PLANTING 151

edge of a metal collecting cup into the bark at each
day's tapping may lead to injury, and is not to be
encouraged.

In all operations dealing with latex the utmost
attention must be paid to the virtue of cleanliness.
Latex is as easily contaminated as milk, a substance
with which it has many properties in common. Not
only should the standard of cleanliness in the factory
be at least equal to that adopted in an up-to-date dairy,
but the avoidance of all kinds of dirt should begin from
the moment when the latex first makes its appearance
upon the surface of the tree. Collecting cups, paring
knives, and the bark itself should all be kept scrupulously
clean. All scrap should be carefully removed from the
tree before paring commences. In order to save the
precious hours of the early morning, this may very
well be done during the afternoon of the day before
tapping.

Plantation Yields.

Finally, some idea may be given of the actual yields
of rubber obtained upon estates. The amounts recorded
vary very largely on different properties, but the follow-
ing figures may be taken as representing approximately
the average yields obtained with moderate systems
of tapping in Ceylon and the Malay Peninsula
respectively.

152 RUBBER AND RUBBER PLANTING

TABLE XXIX

Ceylon

Malaya

Age of trees,
years

Per acre,
Ibs.

Per tree,
Ibs.

Per acre,
Ibs.

Per tree,
Ibs.

4— 5
5-6
6- 7
7- 8

50

100

150

200

'4
•6
•8

I "2

100

150

200
250

•8
ro

i'3
r6

8-9

250

I'S

350

2'2

9 — 10

300

i*9

400

2'5

Very much higher yields than these have been
obtained under favourable conditions, and larger average
yields may probably be anticipated in later years,
now that the importance of careful and moderate
tapping during the early stages is beginning to be fully
realised.

CHAPTER VII

FACTORY WORK ON THE ESTATE

General.

THE latex, brought to the factory in tanks or buckets
as it is collected from the trees, contains as a rule from
30 to 40 per cent, of pure caoutchouc. The latter is
obtained in a state of considerable purity by the
successive processes of coagulation, washing and drying.
The method of preparing biscuit rubber by hand, as
practised during the earliest beginnings of the industry,
is now of little more than historical interest. It may
serve however to illustrate in their simplest form the
nature of the chief processes concerned.

In this method the latex is first strained through
a brass or copper wire sieve of small gauge, and then
generally diluted with one or more times its own bulk of
water. The diluted latex is next agitated with a dilute
solution of acetic acid, containing about one volume of
pure acid for every 1000 volumes of pure latex. The
acidified latex is then poured into round shallow pans to
set. Coagulation begins almost immediately, but the

154 RUBBER AND

pans are allowed to stand for several hours until a
firm cake of rubber of the consistency of cream cheese
has formed upon the surface. The remaining liquid is
by this time perfectly clear and free from rubber. The
cake of rubber is then removed, washed in clean water,
and rolled out thin on a board with a common rolling
pin or a bottle, in order to express as much water
as possible. The resulting biscuits are then spread out
to dry on racks in an airy and darkened room. In
favourable weather the drying may be complete in from
15 to 20 days, if the biscuits do not exceed one-tenth
of an inch in thickness. The resulting product con-
sists of thin round sheets of rubber. If all goes well,
the biscuits are semi-transparent and of a uniform honey
colour.

The first step towards more elaborate processes of
manufacture was the substitution of a simple rolling
machine for the bottle or rolling pin ; but with the
increase of crops from large estates, hand labour has
largely been ousted by the introduction of heavy
machinery.

The Factory,

The site for the factory should combine a central
position on the estate with accessibility to the main road
or other means of transit leading to the port of ship-
ment. A plentiful supply of good clean water is
essential for washing. It is generally best for the
factory to lie at the lowest possible level, since the

RUBBER PLANTING 155

incoming latex is heavier for transit than the outgoing
rubber. Water power should be made use of if avail-
able, but this is comparatively rare on rubber estates.
The source of power usually employed consists of steam
or suction gas or liquid fuel engines, of which the latter
are probably the more popular. A supply of steam may
however be required for heating purposes.

The amount of power required depends upon the
size of the estate. On a plantation of 500 acres pro-
vision will have to be made for turning out 1000 pounds
of dry rubber daily at certain seasons of the year. The
treatment of the latex cannot be delayed, and machinery
must be available for dealing with the maximum crop
at any season. For this output about 45 horse power
will be required for the washing and creping machines,
in addition to about 8 horse power for vacuum driers, if
these are adopted.

Several firms of engineers now specialize in the
building of rubber factories and in the provision of
suitable machinery. The details of structure and equip-
ment best adapted to the needs of any particular estate
can best be settled in consultation with a reliable firm.
One of the most important details to be considered
relates to the lighting of the factory. Plenty of light is
desirable for working the washing, rolling and creping
machines, but in the subsequent stages of the process of
manufacture an excess of light is to be avoided, owing
to the injurious effect of light upon the rubber. Rooms
intended for the drying and storage of the rubber

156 RUBBER AND

require to be specially well screened from light, either
by curtains or by painting the glass of the windows.
It is usual to begin with a factory of moderate size,
which is capable of expansion as the crops of rubber
increase ; and it should be borne in mind when drawing
up the original plans, that provision may ultimately have
to be made for dealing with a crop of more than two
pounds of rubber daily from every acre of the planted
area. Another essential point is the necessity for the
utmost cleanliness at every stage of manufacture. Any
carelessness in this respect is liable to lead to the pro-
duction of discoloured or even tacky rubber, with a
corresponding diminution in the value of the product.
It is worth while to copy from modern hospital buildings
the method of rounding off all corners where walls and
floors meet. Internal surfaces, wherever possible, should
be of smooth cement. Floors should be sloped so
as to drain into cemented channels for greater ease in
washing. A plentiful supply of clean water is essential.

Transport of Latex.

The latex is generally brought in from the field by
coolies in enamelled iron buckets. On very large
estates wheeled tanks are sometimes employed, and in
some cases a system of small tram lines or monorails
has been resorted to. Where the bulk of latex to
be dealt with is very great, coagulation is often carried
out in sheds in the rubber fields, and the wet rubber

RUBBER PLANTING 157

thus obtained is transported to the central factory for
further treatment.

Coagulation.

The principal medium employed for effecting coagu-
lation is acetic acid. Other coagulants are sometimes
employed. The merits of hydrofluoric acid have been
widely advertised, but the powerfully corrosive effect of
this substance is a disadvantage. We do not know
of any exhaustive comparison between the effects of
hydrofluoric acid and those of acetic acid. Mixtures
containing tartar emetic, formaldehyde and other sub-
stances have also been recommended.

Fresh latex is slightly alkaline. The chemical and
physical nature of the process of coagulation is not
altogether understood, but it is generally supposed that
the phenomenon consists primarily in the precipitation
of the proteids of the latex which are soluble in an
alkaline medium. The coagulated proteids form a net-
work in the meshes of which the globules of rubber are
entangled, and the whole then contracts into a clot. An
excess of acid leads to renewed solution of the proteids,
so that either too much or too little acid produces
incomplete coagulation. The special merit of acetic
acid lies in the wide range of proportions in which it
can be added to the latex, whilst still ensuring complete
coagulation. Thus Parkin states that the acid can be
added either in quantities four times below the proper
amount or nine times above it, with very little waste of

158 RUBBER AND

rubber. Acetic acid has also less destructive effect on
the finished rubber than most of the mineral acids. It
is generally recognised however that an excess even of
acetic acid is harmful to the manufactured product. It
is therefore important that only just sufficient acid
should be added to ensure complete coagulation. The
exact amount required appears to vary considerably
under different circumstances. Parkin found that com-
plete coagulation was produced by the addition of
•09 per cent, of pure acetic acid, or one part in about
iioo of pure latex. Working with latex from the old
Henaratgoda trees, we have found that this amount is
often insufficient, whereas on many estates a smaller
proportion is generally found to be effective. It is to be
recommended that in large factories the bulked latex
should frequently be tested on a small scale in glass
vessels, in order to ascertain the smallest amount
necessary. If the latex has been kept for some time,
its alkalinity may be reduced by the action of putre-
factive bacteria, and a smaller amount of acid will then
be required.

The correct amount of acid, well diluted with water,
is added to the latex, which is then thoroughly stirred
and allowed to stand. When crepe is being manu-
factured the coagulation usually takes place in enamelled
buckets. From these the spongy rubber is removed after
an interval of half an hour or less and transferred at
once to the washing machines. For the manufacture of
sheet rubber the latex must be set in shallow pans. In

RUBBER PLANTING 159

these it is allowed to stand for some hours until a firm
clot is formed, which can be lifted out in one piece and
rolled into sheet. The pans vary in depth from 2 to
4 inches, according to the thickness of the sheet required,
and a common size is 9 by 18 inches.

As opposed to coagulation, a centrifugal method of
separating the rubber globules from the latex was sug-
gested some years ago by Bitten. An electrolytic
method of separation has recently been patented by
Cockerill. In addition to these methods, various forms
of mechanical churns and separators have been recom-
mended for use in connection with acid coagulation.
The ordinary method has a considerable advantage
over all the last-named processes in the matter of
simplicity, and it seems likely for the present to hold its
ground. The centrifugal method has however a special
use in dealing with Castilloa. At present the method of
creping is decidedly the most convenient and the most
rapid for dealing with large quantities of latex.

Washing.

The majority of commercial rubber, as purchased by
the manufacturer, contains numerous impurities in
various proportions. The first step in dealing with
all wild rubbers is therefore to subject them to a
thorough process of washing and purification. The
following mean values of the loss in weight on
washing are given by Weber for different commercial
rubbers.

160 RUBBER AND

TABLE XXX.

Loss of weight of rubber samples on washing.

Trade name Loss, per cent.
Para, hard cure 15

Congo Ball 28

Ceara (Manicoba) 32

Borneo 48

One of the chief merits of plantation rubber from
the point of view of the manufacturer lies in its high
degree of purity, and the very small loss which conse-
quently results when it is subjected to the washing
process. In fact, in the near future, manufacturers who
deal exclusively with plantation rubber will probably
be able to omit the preliminary washing process
altogether.

Owing to the clean character of the latex brought in
to the factory on an estate, mere coagulation and drying
would lead to the production of a rubber of a higher
degree of purity than any wild kind. Washing is
necessary however in order to remove the residue of the
acid left over after coagulation, together with the soluble
constituents of the latex. The latter serve no useful
purpose, and are liable if retained to act as nutriment
for moulds and bacteria.

The washing machines employed on estates are
generally similar to those used by rubber manufacturers,
but are constructed on a somewhat smaller scale. Such
machines consist essentially of a pair of heavy steel
rollers which revolve in opposite directions. The hand

RUBBER PLANTING 161

roller illustrated shows all the essential features of
heavier machines which are driven by belts or shafting.
The distance between the rollers is adjustable by special
screws. A spray of water plays over the rollers, and a
strainer is placed below the machine in order to collect
any fragments of rubber which may be torn off in the

Fig. 22. Hand washing machine.

washing process. [Three types of machine, differing
somewhat in detail, are employed for different purposes,
namely sheeting, creping and macerating respectively.

Sheeting machines have smooth rollers which revolve
at an equal rate of speed. The rubber sheets are simply
passed two or three times between the rollers under a

L II

162 RUBBER AND

stream of water. The washing of sheet rubber is there-
fore largely superficial.

Creping machines have grooved rollers which revolve
at different rates. The grooves may be arranged in a
diamond pattern, or the roller may have plain parallel
grooves disposed either longitudinally or in a slight
spiral. The relative rates of revolution of the rollers
varies between 2 : 1 and 6:5. When the rubber is passed
between such rollers, set fairly close together, under a
stream of water, the rubber is stretched and torn and
the washing is much more complete than if the rollers
revolved at an equal rate. The rubber leaves the
machine in a long lace-like strip, which is a convenient
form for rapid drying.

Macerating machines are similar to creping machines,
but have coarse grooves and a high differential rate of
speed. They are employed in the preparation of crepe
from bark-shavings and other sources where there is a
large amount of impurity to be removed.

Drying.

The simplest method of drying the rubber is to hang
up the strips of crepe or sheets in a large and airy room.
Light must be carefully excluded from the drying room,
and thorough ventilation must be provided for. In the
moist climates in which rubber is generally grown,
drying is a very long process unless artificial means are
employed for removing the moisture of the surrounding

Plate VIII

RUBBER PLANTING 163

air. In practice the use of hot air is often adopted, the
method being based on the processes customary in tea-
withering lofts and in cacao-curing houses. Prolonged
exposure to a high temperature is not however to be
generally recommended, owing to the softening effect
upon the rubber, and the danger that tackiness may
arise. The use of cool air artificially dried has been sug-
gested, such drying being effected either by mechanical
cooling or by the use of such a substance as calcium
chloride. However, the technical difficulties in the way
of adopting such a process have not been entirely
overcome, and the method is scarcely used in practice.
The most rapid and convenient way of removing the
moisture is by the use of vacuum driers. In these
machines the thinly creped rubber is spread on trays in
a square chamber or oven provided with a door which
can be shut quite air tight. The chamber is heated by
steam to a temperature of about 90 degrees F. It is
then exhausted by means of a powerful air pump, and
the pressure is kept low in this way for one or two
hours. A large machine is capable of dealing with 200
to 300 Ibs. of rubber in two hours. The rubber is taken
from the drier in a soft and woolly condition, and is
generally re-creped whilst still warm. It should be
pointed out that certain manufacturers are of opinion
that rubber dried in this way is inferior in nerve to
samples slowly dried in the open. Other experts how-
ever consider vacuum-dried rubber to be as good as any
other.

ii-

1 64 RUBBER AND

In fact, from the fluctuations in market price of the
different forms of plantation rubber, it may be concluded
that manufacturers have not yet arrived at a unanimous
preference for any particular method of preparation.
At successive auctions the market may be headed by
pale crepe, block rubber, smoked sheet or by some other
form. From the planter's point of view, creping and
vacuum drying are probably the most convenient
methods. It may therefore be useful briefly to recapitu-
late the successive processes gone through in an
up-to-date factory in which these processes are employed.
Although objections have been made to both these
processes on account of their effect on the mysterious
quality known as nerve, yet both are closely similar
to some forms of treatment which the manufacturer
himself employs. It seems probable therefore that
objections to these methods will fade away as soon as
large bulks which have been " worked " to an equal and
known extent can be put upon the market.

Creping and Vacuum Drying.

In a typical factory then, the spongy mass of rubber
derived from the acidified latex is fed into the first
washing machine. The rubber is passed repeatedly
through this machine under a stream of water, and
finally emerges as fairly thick crepe. This cr£pe is
passed through a second machine in which the rollers
are closely set, and is converted into a continuous strip

RUBBER PLANTING 165

of very thin or lace cr£pe. The thin wet crepe is
arranged in thin layers on the trays of the vacuum
drier, and when all are full the door of the oven is
secured and the pumping machinery set to work. From
the vacuum drier the rubber emerges after a couple of
hours in a fluffy condition, looking very much like a
blanket — much more so than the blanket crepe into
which it is next converted by passing repeatedly
through a machine in which the rollers are set fairly
wide apart. The crepe is finally cut up into lengths
convenient for packing in boxes, which contain from one
to two cwts. of rubber.

An objection to crepe, as usually exported at
present, lies in the fact that it does not bear the brand
of the estate impressed upon the rubber ; whereas sheet
and block rubber is regularly marked in this way. A
machine could easily be devised for stamping the sheets
of crepe at frequent intervals, and the use of some such
method is strongly to be recommended.

Smoking.

It is not uncommon to combine the slow drying
of rubber with a process of smoke curing, and for some
time past rubber prepared in this way has commanded
a higher price than the unsmoked variety. Many
buyers believe that the creosote and other substances
contained in the smoke exercise a preservative and
strengthening effect upon the rubber. The curing of

1 66 RUBBER AND

the wet rubber after sheeting or creping is a process
essentially similar to the curing of hams or of herrings.
The strips of rubber are hung up in a drying chamber
which is impregnated with smoke from a fire fed with
green wood or coconut husks. It is usual to have the
smoking house separate from the main factory in order
to avoid danger from fire.

Smoking of Latex.

Various methods of preparing rubber by the direct
action of smoke upon the latex have been suggested
in imitation of the preparation of Hard Para rubber in
Brazil ; and a variety of machines have been devised for
this purpose. Such methods of preparation are at
present only tentative. Before they can be definitely
recommended, further reports are required both on the
quality of the rubber prepared in this way and on the
facilities for adopting the method on a large scale in
factories. It may be added that the last named
necessity is one which inventors frequently seem to
lose sight of.

In a machine devised by Mr H. A. Wickham the
latex is allowed to flow upon the inner surface of a
rotating cylinder, where it forms a thin film and is
exposed to a jet of smoke obtained by burning coconut
shells in a special stove. The rotation of the cylinder is
so arranged that as each film of latex sets, another film
is spread over its inner surface and is exposed in its

RUBBER PLANTING 167

turn to the smoke fumes. When a certain thickness of
semi-solid rubber has been obtained, this is scraped out
of the cylinder and pressed into a block. Rubber pre-
pared in this way contains all the constituents of the
latex, including a considerable percentage of water, and
may be expected to resemble the Brazilian product
closely. The chief point which still requires to be
settled is how such rubber will compare in its physical
properties with hard-cured Para on the one hand and
with the usual forms of plantation rubber on the other
hand. Rubber prepared by a somewhat similar method
at the Singapore Botanic Gardens has been reported on
very favourably by the manufacturers, but one or two
experiments are not sufficient to establish the value of
the method as compared with other processes already in
operation on plantations.

Blocking.

Blocks of rubber are prepared in special pres'ses by
combining several layers of sheet or crepe rubber, either
smoked or unsmoked. Block rubber has the advantage
of being very convenient for transport, and is also less
liable to undergo damage during transit. From the
point of view of the manufacturer, large blocks of rubber
possess two disadvantages. It is necessary to cut up the
blocks into smaller pieces before the rubber can be
further dealt with in the factory. The presence of
impurities or adulterations also cannot be detected

1 68 RUBBER AND

simply by external inspection. Both these objections
can be overcome by making flat blocks, which should
not be more than one or two inches in thickness. Such
blocks however are somewhat more troublesome to make
than thick ones.

Scrap Rubber.

The highest grade of rubber prepared from the
strained latex is known as First Latex Rubber. Other
grades are prepared from the strainings of the latex,
from the scraps of rubber which have dried on the bark
of the trees or in the collecting cups, from the shavings
of bark removed in paring, and even from the latex
which has dried upon the ground beneath the trees.
The scrap from small estates is sometimes sold as such,
but on large estates the whole of it is turned into crepe
of various grades, according to the colour and the
amount of impurity remaining after the washing pro-
cess. After passing repeatedly through the macerating
machines, the greater part of the impurities present are
washed away, and the value of the rubber thus produced
is only 20 or 30 per cent, less than that of First Latex
Crepe.

Packing.

The rubber is packed in wooden cases containing
generally between I and \\ cwts. It is most important
that the inside of the cases should be smoothly planed
and perfectly clean, and that no packing material of any

RUBBER PLANTING 169

kind should be used. Anything sticking to the rubber
at once detracts from its value. The presence of the
smallest amount of impurity may necessitate the
addition of an elaborate process of purification prior
to the other processes of manufacture. Just as in the
case of tea and other products which are paid for by
the pound, it should be the object of the packer,
when making up the cases, to include such an amount
of rubber as will weigh a few ounces more than an even
number of pounds on arrival at its destination. This is
owing to the fact that fractions of a pound are neglected
in favour of the buyers, with the result that looj Ibs.
are paid for as 100, whilst 99f Ibs. are paid for as only
99 Ibs. With rubber at four shillings a pound the
matter is worth some attention. Some experience is
required for determining just the right amount that
should be included, owing to the fact that rubber is
liable to lose a certain amount of weight in transport.

Sales and Markets.

The largest importing market of the world for
rubber is New York, which receives nearly half of the
total supply. Liverpool and London probably receive
a comparatively higher proportion of the produce from
Eastern plantations, although the value of plantation
rubber is also beginning to be more fully recognised in
New York. The other chief ports concerned in the
rubber trade are Hamburg, Antwerp and Havre. In

i?o RUBBER AND

New York sales are by personal contract for immediate
delivery. In Liverpool and London, auction sales are
held at stated intervals after samples have been exposed
for a certain length of time. Private sales also take
place in London, and a good deal of plantation rubber
is now sold in advance by contract. Fortnightly
auction sales of rubber are also held in Colombo and
in Singapore.

The Best Form of Plantation Rubber.

We have seen that plantation rubber is placed upon
the market in a variety of different forms, among which
biscuit, sheet, crepe and block are the most familiar.
Any of these forms may be either smoked or unsmoked,
and the unsmoked varieties may differ much in colour ;
whilst the thickness and other characteristics of the
different types also vary considerably. It is a curious
fact that whilst one of the principal demands of the
manufacturer is for uniformity in the product which
he buys, the present diversity is partly due to the
failure of the manufacturers to make up their minds
which type they prefer. In this way a vicious circle is
established, and the desire of the producer to turn out
a uniform product is partly frustrated by the buyer.
On the other hand, it must be admitted that similar
grades of rubber, when produced on different estates
and from trees of different ages, appear to differ con-
siderably in strength and resiliency.

RUBBER PLANTING 171

Quality.

Light coloured rubber is valuable for certain
purposes ; for example transparent tubes for feeding
bottles are now made from pale plantation rubber. The
number of uses for which a very pale tint is necessary
is however comparatively small. One obvious advantage
of light coloured transparent rubber lies in the fact that
its purity is unmistakable, as compared with dark com-
mercial rubbers, and until recently a higher price was
commanded by the palest crepe rubbers. The quality
of raw rubber, however, depends mainly upon what is
known as nerve. This expression more or less sums up
the results of tests upon the breaking strain, extensibility
and resiliency, all of which should, generally speaking,
be as high as possible. The resiliency of the rubber is
measured by the pull exerted after a certain period of
extension, and by the permanent extension shown after
a certain period of stretching, followed by a certain
interval of rest. The most resilient rubber exerts a
large pull, and shows a small permanent extension. In
practice, the strength and resiliency of the rubber are
estimated by the brokers simply by handling and
stretching ; and although expert buyers arrive at a high
degree of skill and judgment, such methods cannot be
regarded as infallible. It is even whispered on estates
that thick crepe is preferred to thin on account of its
greater apparent strength. In this particular form of
rubber, strength is a feature particularly difficult to

172 RUBBER AND

determine by rule of thumb methods. A simple and
uniform method of testing commercial samples is there-
fore greatly to be desired. At the present time there is
little doubt that differences in the original samples, and
differences which arise during transport and storage, are
often to some extent discounted by slight inaccuracies
in the methods of testing. The determination of the
best form of plantation rubber is thus further delayed.

It is therefore not surprising that the opinions of
experts seem to differ as regards the precise effect of
almost every factor which is capable of influencing the
quality of the manufactured rubber. Thus rubber from
young trees was formerly regarded as markedly inferior
to that obtained from old trees. Recent experiments
have not invariably confirmed this conclusion, although
some appear to do so, and the question is not finally
settled. In a similar way opinions differ widely as
regards the effect of smoking or the use of vacuum
driers. At present the general opinion is that plantation
rubber is on the whole less satisfactory and less durable
than fine Para. Thus it is commonly stated that plan-
tation rubbers are unsuitable for the manufacture of
elastic thread, a use which is generally admitted to
represent one of the most stringent tests of quality.

As the crops on Eastern estates increase, and larger
and larger bulks of rubber are turned out, a steady
increase in uniformity is to be expected. Already many
samples of plantation rubber have been produced which
are indistinguishable in quality from the best Para by

RUBBER PLANTING 173

all ordinary tests. In fact, there is every reason for
believing that in the future the highest plantation
grades will share with hard Para the distinction of
representing the highest standard of quality, even if
they do not oust the American product from its present
position of superiority.

As regards chemical purity, plantation rubber already
surpasses any wild kind. It is therefore preferred by
manufacturers to any wild rubber for the manufacture
of rubber solutions and for waterproofing.

Defects and Blemishes.

Complaints are not uncommonly made of the
appearance of spots and discoloured patches on the
rubber turned out of the factory. In fairness be it
remarked that such complaints are much less common
than formerly. Fetch states that the chief organisms
concerned in the spotting of rubber biscuits appear to
be bacteria and yeasts. Blood red spots sometimes
appear. These have been attributed to the action of
Bacillus prodigiosus, the microbe responsible for the
so-called bleeding miracles. Brown and black patches
may be due to the attacks of other bacteria. Dis-
colouration may usually be prevented by attention to
perfect cleanliness at every stage of preparation. All
utensils which are brought in contact with the latex
should be frequently scalded with boiling water, and the
factory itself should be kept scrupulously clean. The

174 RUBBER AND

hackneyed comparison with the conditions of an up-to-
date dairy may profitably be borne in mind. The
practice of frequent cleaning should extend to the
tapping tools and collecting cups. It has been recom-
mended that the latter should be of glass or earthenware,
since proper cleansing is difficult with any form of metal
cup. Glass or earthen cups are unfortunately very liable
to be stolen on small estates.

The growth of mould fungi on the rubber sometimes
causes trouble in wet weather. As a rule little damage
is done in this way, the action being entirely superficial.
Moulds seldom appear in large factories where the
preparation is rapid and the storing and packing rooms
are kept dry. Smoked rubber is practically immune
from the attacks of moulds, owing to the antiseptic
properties of the smoke constituents.

Tackiness.

Rubber is said to become tacky when the surface
turns soft and sticky. In some cases the softening may
proceed so far that whole sections of rubber fall to pieces
and dissolve into a liquid form. Tacky rubber is useless
for the ordinary purposes of manufacture, and can only
be sold at a low price as a subsidiary product. The
condition is rightly dreaded as the worst defect which
can possibly arise.

One certain cause of tackiness is exposure to sun-
light, and it is to guard against tackiness that drying

RUBBER PLANTING 175

and storing rooms must be carefully guarded from
excessive light. According to Fetch, the assertion that
tackiness can also be caused by the action of bacteria
has not been conclusively proved. It is quite possible
however that tackiness exists in different forms, and may
be due to different causes. The use of too strong acid
in coagulation may lead to tackiness, and it is generally
believed that the condition arises more readily if the
acid employed in coagulation is not thoroughly washed
out of the rubber. Heat has also been mentioned as a
cause, although the softening due to a high temperature
is usually temporary, and passes off when the rubber is
cooled. The fact is that the conditions which lead to
tackiness are by no means fully understood, and further
study is desirable.

CHAPTER VIII

THE PESTS AND DISEASES OF HRVEA

Plantation Conditions.

PROBABLY no species of plant is exempt from the
attacks of some kind of animal or vegetable enemy or
parasite. Under natural conditions, however, it is rare
to find any disease developing the proportions of an
epidemic and killing off large numbers of plants in a
particular area. In the case of tropical trees like Hevea,
one very good reason for the absence of epidemics
under the ordinary conditions of forest growth is readily
discernible. Unlike the uniform woods characteristic of
temperate climates, a tropical forest almost invariably
consists of a varied mixture of different species of trees.
This mixed character of tropical vegetation extends so
far that it has been estimated that as many as three
hundred different species of trees are often to be found
on a single acre of ground, whilst two individuals of the
same species practically never stand side by side.

The conditions obtaining in a plantation are pre-
cisely the reverse of those natural to a tropical forest.

RUBBER AND RUBBER PLANTING 177

Hundreds of thousands of trees of the same species are
here arranged in regular rows, their leaves and roots
actually intermingling. The conditions are therefore
ideal for the development into an epidemic of any
disease which may make its appearance.

Epidemics.

Consequently the occurrence of epidemics under the
conditions described is by no means unknown. One of
the most famous examples of modern times is afforded
by the coffee leaf fungus Hemileia vastatrix, which, in
combination with other diseases, entirely ruined the
coffee planting industry of Ceylon in the seventies and
early eighties. This calamity has taught planters in
general a lesson which it is to be hoped they will not
readily forget; for if a disease be taken in hand in its
early stages, when only a few individuals are affected, it
is generally possible to cope with the trouble to some
extent and to prevent its universal spread. With this
object in view, superintendents are now instructed to
keep a close look-out for the first indications of disease;
and expert plant-doctors — entomologists and mycolo-
gists — are maintained in all important tropical planting
countries. It is their business to diagnose correctly any
symptoms of disease which may appear, and to prescribe
the most appropriate remedies which science has been
able to devise.

And, just as in the case of human ailments, the
L. 12

i;8 RUBBER AND

general practitioner is relied upon for the treatment
of well-known complaints, but the scientific specialist
is called in where the cases are difficult to diagnose, so
it should be in the case of plant diseases. For every-
day work the planter is his own doctor, and a good
planter should be familiar with the nature and treatment
of the common diseases to which his crop is liable.
The recognition of new diseases and the devising of
appropriate remedies calls for scientific research by
highly qualified specialists. No community of planters
can regard itself as safe from the danger of new diseases
which does not maintain a properly equipped establish-
ment for research, headed by a scientific officer of the
highest possible qualifications. Probably in no branch
of commercial enterprise does the liberal treatment of
science pay better than in planting.

Hitherto no disease of Hevea has assumed the
proportions of a serious epidemic, and we have no
reason for anticipating that a fate similar to that of
coffee in Ceylon awaits this industry in any country
where rubber is now cultivated. Minor ailments exist
however in some variety, and it behoves the planter as
well as the agricultural official to familiarise himself
with the known symptoms of disease and with the
simpler recognised remedies. He can then take
immediate steps to prevent the wide extension of
trouble from small beginnings ; serious trouble is only
likely to occur if unhealthy individuals are neglected.
As prevention is better than cure, an elementary

RUBBER PLANTING 179

knowledge of the general principles of plant sanitation
is even more important than a knowledge of special
diseases.

Wind.

Perhaps the most serious of all pests which affect
the health of rubber plantations is an inanimate one,
namely wind. In regions which are severely wind-swept
it is useless to attempt the growth of Hevea rubber. In
less exposed situations the force of the wind may be
broken by leaving belts of jungle when the original
clearing is carried out, or by planting rows of hardy and
quick-growing trees as special wind-breaks. The idea
of jungle belts has frequently been suggested as a
means of checking the spread of fungus diseases, but
it appears to have been very seldom carried into effect,
the planter preferring to occupy the whole space at his
disposal with his own proper crop. Such belts more-
over possess this serious disadvantage; that if they are
wide enough to prevent the passage of wind-borne
fungus spores they are also large enough to afford an
excellent harbourage for weeds and for many of the
vertebrate enemies mentioned in the next paragraph.

Animals.

Among the larger animal pests of rubber plantations
are elephants, deer, cattle, pigs, monkeys and porcupines.
All these animals are liable to effect widespread destruc-
tion in young clearings, and porcupines may even cause

12 — 2

i8o RUBBER AND

serious damage to adult trees by gnawing off the bark.
A good deal can be done by fencing to exclude all the
above-named animals with the exception of monkeys,
but in order to be effective the fencing must be very
thoroughly carried out. Deer can easily clear a six-foot
fence, whilst barbed wire is a matter of supreme in-
difference to an elephant who has made up his mind
to proceed in a certain direction. The lower part of the
fence must be of wire netting if porcupines are to be
excluded.

Insects.

Under ordinary conditions a healthy Hevea tree is
practically immune from the attacks of boring insects,
owing to the presence of latex, which is found an effectual
check to the progress of these pests. If, on the other
hand, an area of bark is killed by wounding or by the
attacks of fungi, the latex soon dries up. Boring
beetles and other insects then readily obtain access,
and contribute materially to the damage done to the
tree. The insect attacks are however purely secondary,
and t*heir prevention is essentially bound up with that
of the original cause of damage, which is usually a
fungus disease.

There is however one insect, prevalent in the Malay
Peninsula, which is able to cause considerable damage
to living Hevea trees without the assistance of fungi.
This is a species of white ant known as Termes Gestroi,
which is apparently able to effect an entry through the

RUBBER PLANTING 181

roots of entirely healthy trees. The insects then rapidly
proceed to eat out the interior of the wood. Termes
Gestroi is a pest which requires to be seriously taken in
hand at its very first appearance. By digging a shallow
trench round an affected tree it is often possible to
locate the position of the termites' nest, because the
insects quickly build covered ways across the bottom of
the trench in order to obtain access to their food supply,
and by following these up the direction of the nest can
be determined. The best means of exterminating the
white ants is by pumping into their nests the fumes
of sulphur and white arsenic, generated by heating
these substances over burning charcoal in a special
apparatus. The channels excavated in the affected tree
may be similarly fumigated, but if the damage has pro-
ceeded far it is simpler and more effective to cut down
the whole tree and burn it.

In its early stages of growth Hevea is susceptible to
the attacks of a somewhat larger variety of insect pests.
Young plants in nurseries, and those which have recently
been planted out in clearings, are subject to damage
from cockchafer grubs, cutworms and similar sub-
terranean creatures which gnaw the roots. These may
be got rid of to some extent, at least in nurseries, by
treating the soil with kainit or with " vapourite," a
preparation sold for the purpose.

One animal against which the presence of latex is
no protection is a slug — Mariaella Dussumieri — which
actually drinks the latex, and appears to thrive upon a

i82 RUBBER AND

beverage which most animals would find decidedly
indigestible. These slugs may do considerable damage
by eating off the buds and young leaves. They may be
prevented from climbing the trees by painting a band
of tar round the trunk. Another method is to steep
sawdust in a ten per cent, solution of carbolic acid,
and sprinkle it round the bases of the trees. Such
measures, in addition to protecting the trees for the
time being, soon lead to a diminution in the numbers of
the pest by cutting off the latter from its principal
supply of food.

Fungus Diseases.

On the whole, the enemies of Hevea belonging to
the animal kingdom are less deadly than the vegetable
pests reckoned among the parasitic fungi. The most
important, that is to say the commonest, diseases of
Hevea which are due to the attacks of fungi, are five in
number. These may be divided into two groups,
according to their point of attack. Two of the common
diseases attack the roots, whilst three of them are found
upon the trunk or branches. One of the most serious
of the latter also attacks the fruits. In addition to
these, there are a number of other diseases which are of
smaller importance from the planters' point of view,
either because of their rarity or because the damage
hitherto ascribed to their attacks is insignificant. Such
diseases are however of special interest to the professed
mycologist, whose business it is to study the conditions

RUBBER PLANTING 183

under which they might become more prominent, with a
view to ensuring, if possible, that the necessary con-
ditions do not arise. Some of the fungi in question
attack the roots, others the stems and others again the
leaves, especially in the case of young plants.

Diseases of the Roots.

Root diseases are particularly dangerous, because
their early stages generally pass unnoticed, and very
often the first indication of their presence is given by
the death of the tree. Sometimes the main tap-root
may be entirely destroyed without any sign of injury
appearing above ground, since sufficient supplies of
water and salts are provided by the lateral roots to
maintain the crown of foliage in a condition of apparent
health. One day a storm of wind brings down the
whole tree, and the full extent of the injury is disclosed.
Occasionally a single lateral root may be discovered
showing symptoms of disease. In such a case it may
be possible to cut away the diseased portion and to
save the remainder of the tree. In the majority of
cases, however, the planter must make up his mind to
destroy the affected tree in the hope of saving its
neighbours.

Altogether, three different root diseases are at
present recognised, which may be readily distinguished
from one another on examining the affected roots. In
the case of the fungus known as Pomes semitostus, which

1 84 RUBBER AND

is the most serious of the three, the dead root is found
to be covered with white or yellowish threads and cords
of mycelium — the growing strands of the fungus. An
equally common, but not quite so destructive, fungus is
Hymenochaete noxia, which may be recognised from the
fact that the root killed by it is covered with an
encrustation of sand and small stones, cemented to-
gether by the brown or black mycelium. There is
a third less common fungus which is occasionally found
upon the roots of Hevea in Ceylon, known as Sphaeros-
tilbe repens. When this is present there is no external
mycelium on the surface of the root, but on peeling off
the bark, dark brown strands of mycelium are found
wandering over the surface of the wood.

Fames semitostus.

The fructification of Fomes semitostus does not
usually make its appearance until long after the death
of the tree. Where rubber trees have died however it is
frequently to be found on a neighbouring jungle stump.
The fructification or sporophore grows out in the form of
a flat semi-circular bracket from the decaying log or
stump. It is distinguishable from innumerable other
" bracket fungi " by its characteristic colours. When
fresh, the upper surface is coloured a rich brown with
a narrow rim of yellow, whilst the under surface is
bright orange. The consistency of the fructification
is woody and brittle, and the lower surface is covered

RUBBER PLANTING 185

with enormous numbers of very minute holes. The
latter represent the openings of the tubes in which the
spores are produced.

According to Fetch, the disease makes its appear-
ance as a rule when the plantation is from one to three
years old. This is due to the fact that the fungus
spores do not attack the living trees directly. The
spores, however, germinate readily on dead jungle
stumps remaining in the soil, and develop a vigorous
mycelium. Stout strands of mycelium, known as
rhizomorphs, then grow out through the soil, and are
able to attack the living roots of Hevea.

When the presence of this disease is recognised in
a plantation — generally owing to the blowing down of
one or more trees — immediate steps must be taken to
destroy the affected trees and to prevent further loss.
The roots of all affected trees must be dug up and
burnt, and in particular the jungle stump in which the
evil originated must be found, dug out and thoroughly
destroyed by fire. When the limits of the group of
affected trees have been ascertained — if necessary by
digging down to examine the roots — a trench from
1 8 inches to two feet in depth should be dug right
round the affected area. The earth removed in digging
should be thrown inside the trench. The ground
enclosed within the trench should be deeply dug all
over and lime forked in, and the bottom of the trench,
which must be kept clear of weeds, should be covered
with the same material. Fetch does not recommend

1 86 RUBBER AND

replanting with Hevea in less than twelve months from
the date of destroying the diseased trees. This method
of isolating an infected area by trenching was first pro-
posed by Hartig for use in forestry work. It was
recommended by Massee for dealing with Rosellinia in
tea.

Hymenochaete noxia.

The fructification of Hymenochaete noxia — commonly
known as Brown Root Disease — is much less conspicuous
than that of Femes, and is also comparatively rare.
When present it takes the form of a thin brown crust
adhering to the base of the trunk. The surface of the
crust is velvety, being covered with almost microscopical
bristles. The disease is not confined to Hevea, but is
also found on Castilloa, tea, cacao, camphor, coca and
the shade tree Erythrina lithosperma (dadap) in Ceylon ;
on Funtumia on the Gold Coast and on coffee in Java.
The majority of cases affecting Hevea in Ceylon have
occurred where old cacao has been cleared in order
to plant rubber. Unlike Fomes, the fungus does not
appear to travel independently through the soil, but is
-only transmitted where the roots are in contact with
other diseased roots or with dead wood upon which the
fungus is growing. In order to prevent the appearance
of the disease, the stumps of cacao which have been cut
down in order to make way for rubber should be care-
fully extracted. Hevea trees killed by the fungus should
be cut down and the roots dug up and burnt. The soil

RUBBER PLANTING 187

which the roots of the dead tree occupied should be dug
over and quicklime forked in, but the elaborate pre-
cautions recommended in the case of Fames do not
appear to be necessary, as the fungus seldom spreads
after the source of infection has been removed.

On the other hand, if Sphaerostilbe makes its appear-
ance, the treatment recommended for Fames should be
carefully carried out, since this fungus, too, is able to
spread through the soil to adjacent trees by means of a
free-growing mycelium.

Diseases of the Stem — Canker.

Three diseases of the stem are more or less prevalent
in Hevea, whilst four others which at present appear
to be of minor importance have been recorded from
time to time.

Probably the most serious of the stem diseases is the
so-called canker, which has recently been shown to be
due to the attacks of the fungus Phytophthora Faberi,
and is therefore a near relative of the deadly potato
disease. Like the potato disease, the canker of rubber
is disseminated by motile spores, which swim actively in
the film of water which may cover the surface of the
trunk in wet weather. The canker of rubber has been
shown to be identical with that of cacao, and the same
fungus attacks the fruits as well as the bark in both
species. The term canker is a singularly unsuitable one
for this disease,' which gives rise to no roughness or

i88 RUBBER AND

eruptive outgrowth such as is usually associated with
the name of canker. The disease consists in a softening
and rotting of the inner layers of bark, which may
be scarcely visible from the exterior, or may betray its
presence by the oozing out of a dark red liquid. The
softened and discoloured area is occupied by the hyphae
of the destructive fungus. The rotting bark may soon
become the breeding ground for other fungi, but the
Phytophthora is the primary cause of the mischief. On
shaving off the outer layers of bark with a sharp knife,
the diseased area becomes recognisable as a brownish or
claret coloured patch, with well defined edges separating
it from the surrounding healthy bark.

The only remedy is excision. If the disease is dis-
covered whilst the patch is still small, the whole of the
diseased tissue can be cut away. The healthy bark
should be trimmed all round the exposed area of wood
with a very clean cut, and if much wood is exposed the
latter should be tarred. In the course of time the bark
will heal over the wounded area and the tree will
recover. The disease is specially serious, owing to the
fact that it generally attacks the lower part of the trunk
where tapping is in progress. Tapping must therefore
be suspended until the recovery of the tree is well
advanced. In cases where the disease has already
spread far round the circumference, it is better to cut
down the tree at once. Any diseased portions cut away,
and, in the case of felling, the whole tree, should always
be destroyed by fire.

Plate IX

Photo T. Petch

Canker of Hevea Bark

RUBBER PLANTING 189

The same fungus attacks the fruits of Hevea,
especially in wet seasons. The pods turn black and
sodden, and rot upon the trees. Beyond the loss of the
seed crop, little harm appears to be done directly to the
trees, but the diseased pods serve as centres of infection,
and thus increase the chance of the disease developing
upon the bark. The only possible treatment is to collect
and burn the diseased fruits.

The spread of canker is greatly facilitated by the
shade consequent upon close planting. In districts
where the disease is prevalent it is therefore desirable
that the trees should be widely spaced. Where they are
already closely planted, the question of thinning out
becomes a serious one, but if it is decided to fell a
certain proportion of the trees, the stumps and larger
roots should also be extracted in order to avoid danger
from root disease. It is understood that experiments
are being tried in Ceylon to find out whether the
tapping area can be sprayed with some substance which
will prevent the germination of the fungus spores, whilst
not injuring the quality of the rubber prepared from the
latex. Such spraying is not likely to be of much use so
long as rain water is allowed to flow over the surface of
the tree, whilst, if the trunk can be kept dry, the germi-
nation of spores will probably be checked as effectively
as by a fungicide. The provision of rain guttering
above the tapping area seems therefore to be a most
desirable measure in all districts where rubber canker is
prevalent.

190 RUBBER AND

Pink Disease.

The malady known as Pink disease, due to the
attacks of the fungus Corticium salmonicolor, has much
more the appearance of what is commonly regarded as
a canker. This disease makes its appearance as a pink
incrustation covering the bark. The patch may extend
until it covers a large area, in the centre of which the
bark is dead and dry, whilst at the edges the advancing
fungus is only superficial. Spores are formed upon the
surface of the pink patch, and are carried by the wind
until they find a lodgement upon the surface of the
bark. This commonly occurs at a point where the
trunk forks into two or more branches, and it is in such
a position that the disease generally arises. Hyphae
from the germinating spores penetrate into the bark
and destroy its living tissue. From the centre thus
established the disease then spreads widely over the
surface.

The disease is readily recognisable owing to the pink
colouration which it produces. When the fungus makes
its appearance upon the upper branches of a young tree,
the diseased branches may be cut off completely and
burnt. On older trees, as in the case of canker, it is
sometimes possible to cut out the diseased patch of
bark, if the presence of the fungus is recognised at a
sufficiently early stage. In South India the application
of Bordeaux mixture is widely adopted as a preventive
measure. The fungicide is simply painted on to the

RUBBER PLANTING 191

trees with a brush. This remedy is found to be effective,
and the cost of application is small in comparison with
the value of the immunity obtained. Bordeaux mixture
is made by dissolving 5 Ibs. of copper sulphate in
25 gallons of water in a wooden barrel, and pouring
this solution into a large vessel simultaneously with a
like amount of milk of lime. The mixture must be
continuously stirred during the process. The milk of
lime is prepared by pouring water very gradually upon
5 Ibs. of quicklime, with constant stirring, the slaked
lime being finally made up to 25 gallons. Theoretically,
the amount of lime should be rather less than that
of the copper sulphate, but in practice perfectly pure
quicklime is not obtainable, so that some margin may be
allowed.

Die-Back.

A third disease which attacks the leading shoots of
Hevea is known as die-back. This expression describes
the nature of the disease with considerable accuracy.
The fungus responsible for the disease is known as
Gloeosporium alborubrum. This fungus is microscopic,
and its presence can only be recognised from its results.
These, however, are not generally serious unless the
dead shoots are attacked by another fungus, Botryodi-
plodia theobromae, which, as a rule, cannot by itself
attack living shoots.

When only the first named fungus is present, the
dying back of the stem is confined to the leading

192 RUBBER AND

shoots ; fresh shoots grow out from buds lower down
the stem to take the place of the dead branches, and
but little damage is done. But when the Botryodiplodia
obtains a footing, the disease pursues its downward way
with great rapidity, and ultimately destroys the whole
tree. Here, again, the only remedy is to cut off and
burn the diseased portion. This should be done with a
clean cut some distance below the lowest signs of injury,
and the cut surface should be tarred.

Botryodiplodia has also been known to attack young
stumps shortly after planting. In such cases the fungus
probably effects an entrance through injuries in the stem
or upper part of the root. The holes in which the trees
are planted should in such cases be treated with lime
before supplying with fresh plants.

Burrs and Nodules.

A common complaint affecting the stems of Hevea
trees, to which no sufficient cause has yet been assigned,
consists in the development of woody nodules in the
bark. These sometimes make their appearance upon a
large number of trees at particular periods in a manner
highly suggestive of an epidemic, and grow so rapidly
as to interfere seriously with the operation of tapping.
Hitherto it has not been found possible to show that
the nodules are associated with any specific organism
attacking the bark ; nor are they constantly associated
with mechanical injury, although there is evidence to

Plate X

Nodules in Hevea Bark

RUBBER PLANTING 193

show that they appear in greater numbers on trees
which have been tapped with a pricking instrument
than on trees which have only been pared. In fact, the
whole subject of their origin seems to require further
investigation.

The nodules arise as minute woody bodies buried
in the growing bark, quite independently of the proper
wood of the tree. Their presence is first betrayed by a
swelling and cracking of the outer bark. If the surface
of such a swelling is sliced off with a sharp knife,
numerous nodules, about the size of small peas, are
found embedded in the bark. At this stage they may
be carefully extracted with the point of a knife, and if
this extraction is carried out with thoroughness the bark
recovers and no further injury is done. If neglected,
however, the nodules grow with great rapidity, and fuse
with one another and with the actual wood of the tree.
The surface of the tree now shows extensive rugged
prominences over which tapping by the ordinary process
of paring is no longer possible. The woody mass may
still be prized off with a hatchet or a crow-bar, but
a ragged and extensive wound is left which takes a long
time to heal.

At certain seasons these nodules have appeared on
large numbers of trees all over Ceylon. At other times
their appearance may pass almost unrecorded for years
together. It was observed that the worst visitation
occurred after a prolonged period of drought, and was
most severe at high elevations and on trees which had
L, 13

i94 RUBBER AND

been severely tapped, especially where the pricker had
been employed. The appearance of the nodules is
therefore apparently facilitated by anything which tends
to weaken the vitality of the trees.

The outbreak in question occurred in the spring of
1911. At this time a marked difference in the severity
of the epidemic was observed on two similar plots of
Hevea trees at Peradeniya, each one acre in extent. On
plot A upwards of 60 per cent, of the trees were affected,
and on plot B only about 10 per cent. Plot A had
received during the two preceding years applications of
a concentrated mixture containing 1 50 Ibs. of sulphate
of ammonia, 100 Ibs. concentrated superphosphate and
100 Ibs. sulphate of potash. Plot B was un manured.
During the twelve months immediately preceding the
outbreak, plot A had been tapped by paring and
pricking with the spur-shaped pricker, whilst the trees
on plot B were pared only — on a similar system. It
seems natural to associate the larger proportion of
nodular outgrowths on plot A rather with the pricking
than with the manuring, but it is apparent that the
whole subject requires further study.

General Sanitation.

In a well lighted plantation which is kept clear
of decaying stumps and branches, fungus diseases are
not likely to make their appearance except sporadically.
Close planting and the presence of intercrops produce
conditions favourable for the introduction and spread of

RUBBER PLANTING 195

stem and leaf diseases, whilst decaying stumps remain-
ing in the soil constitute a fruitful source of fungus
diseases of the roots. Fetch, in fact, goes so far as
to state that if there were no dead stumps there would
be no root diseases either in Hevea or tea. The
conclusions to be drawn from these facts are obvious,
but they apply mainly to the precautions which ought
to be taken during the first opening up of the estate.
We have now to consider the sanitation of an estate in
bearing.

On well managed plantations a special gang of
labourers is often employed, whose business it is to
make the circuit of the estate and to keep a close look
out for the appearance of disease. This periodical
inspection is specially necessary in districts subject to
the attacks of die-back and pink disease, since these
maladies may readily escape the attention of the tapping
coolies. In such districts the removal of dead branches
should constantly be carried out as fast as death over-
takes them, and by this means the spread of the diseases
may be reduced to a minimum. The pruning of lateral
branches should always be done by means of a clean
cut flush with the surface of the parent stem, in order
that no projecting portion may be left to die back and
offer a point of entry for disease germs. All extensive
areas of exposed wood should be covered with tar. For
this purpose ordinary gas tar is preferable to Stockholm
tar. All branches and debris removed in pruning should
at once be burned.

13—2

196 RUBBER AND RUBBER PLANTING

For dealing successfully with plant diseases, intelli-
gent cooperation is eminently desirable. A single
neglected and diseased property may constitute a
serious menace to the health of the products on all
the other estates in the same district. The case of an
owner who is not amenable to the principles of co-
operation in the treatment of diseases would constitute
a strong argument in favour of coercive legislation.
For the owner who neglects to take ordinary precautions
for preventing the spread of disease is interfering with
the rights of his neighbour almost as much as if he were
to set fire to a corner of his plantation.

CHAPTER IX

THE CULTIVATION OF SPECIES OTHER THAN
HEVEA BRASILIENSIS

ALTHOUGH Hevea brasiliensis is universally recog-
nised as the plantation rubber tree par excellence y
several other kinds of rubber-producing plants are used
extensively for the same purpose. In spite of its
hardiness, the adaptability of Hevea is limited, and in
dry climates Manihot Glaziovii is probably to be pre-
ferred. In fact, extensive plantations of the last named
species have already been opened in the drier regions
of Africa as well as in its native country, the Ceara
province of Brazil. In the moist climate of West Africa
Funtumia is said to be quite as successful in plantations
as Hevea, although the evidence upon the subject is
somewhat restricted. Finally, in Mexico large planta-
tions of the indigenous Castilloa have been established.
Here, however, it is doubtful whether the planters would
not have been better advised to introduce Hevea, since
the climatic conditions suitable for the two trees are
closely similar.

198 RUBBER AND

Castilloa.

As stated in Chapter I, plants of Castilloa were
brought successfully to Kew prior to the arrival of the
most important consignment of Hevea, and trials have
been made with the former plant in many parts of the
tropics, including almost every British tropical colony.
So far as we are aware, Castilloa has nowhere been
found equal to Hevea in suitability for plantation use,
in spite of fairly exhaustive trials in many different
districts.

The home of the Castilloa tree is Mexico and
Central America. The total export of rubber from
Mexico in 1908 — 1909 was about 1,000,000 Ibs. Of
this amount, some 40 per cent, is stated to have been
plantation rubber. In 1910 the area of rubber planta-
tions in Mexico is believed to have been about 90,000
acres. The greater part of this area was planted
between 1897 and 1906. The capital involved, mostly
subscribed in the United States, was estimated at about
^4,000,000.

So far, these plantations have not by any means
fulfilled the expectations of their promoters. A yield
of 67 Ibs. of dry rubber per acre from six- to eight-year-
old trees, although gathered in at a trifling cost, is very
small compared with the yield from the plantations
of Hevea in the East. The latex from young trees,
moreover, contains a high proportion of resin, and the

RUBBER PLANTING 199

period of waiting for satisfactory crops is consequently
a long one.

The Castilloa has generally been closely planted.
From 200 to 300 trees per acre is by no means an un-
common estimate. Since the growth of Castilloa in the
rich soils of Mexico appears to be considerably more
rapid than the average recorded for Hevea on plantations*
there can be little doubt that the trees are greatly
crowded.

The trees are only tapped at intervals of about four
months. The method employed is purely one of incision,
and consists in cutting a few slanting or V-shaped
channels in the bark. The rubber is usually prepared
from the latex by a process of creaming. In this pro-
cess the latex is diluted with a considerable bulk of
water and, after stirring, is allowed to stand in tanks
until the whole of the rubber has collected as a cream
upon the surface. The clear liquid is then drawn off
from below, and the whole process is repeated until dirt
and soluble impurities have largely been removed. The
rubber is then finally dried and rolled into sheets.
Centrifugal machines are also sometimes employed. In
this way much time can be saved, and the washing is
more completely carried out.

In Ceylon very fine samples of smoked sheet rubber
have been prepared from Castilloa latex. The cultiva-
tion, never very extensive, has however been almost
entirely given up in favour of Hevea. In the West
Indies Castilloa is still under trial, but only on a small

200 RUBBER AND

scale, and the amount of land available for the cultivation
is limited. In Jamaica a yield of 200 Ibs. per acre is
anticipated from Castilloa after the tenth year. This
form of rubber has also been planted somewhat widely
in German colonies, particularly in New Guinea.

In spite of the small yields per acre, Castilloa is still
-regarded by some writers as being the most suitable
form of rubber for plantation purposes in Mexico, owing
to the small cost of collection. Although the total yields
are small, the yield from a single tapping is very much
larger than in the case of Hevea at the same age. The
cost of labour is very much higher in Mexico than in
either Africa or Asia.

Manihot.

Ceara rubber, Manihot Glaziovii, was the third
species to be widely distributed to British possessions
in the Tropics during the seventies. Introduced to Kew
from North East Brazil by Cross in 1876, seeds or plants
were sent out to most of the tropical colonies during the
following year. In Ceylon this species attained a certain
amount of popularity some years before Hevea came to
be at all widely planted. Manihot was planted in the
Trincomalee district in 1880, where, however, in spite of
the richness of the soil, planting has made but little
headway. Nevertheless, in 1883, no less than 977 acres
were under cultivation with this product in Ceylon.

Difficulties of tapping, which have not even now

RUBBER PLANTING 201

been entirely overcome, soon led to a temporary cessa-
tion of planting, and after 1884 the interest in Manihot
died away, owing to the small yields of rubber obtained.
Samples of rubber from Zanzibar were unfavourably
reported on in 1884, and further extension of the
cultivation of Manihot in Africa was thus delayed.
Recently, however, the species has been widely planted
in East and Central Africa and in Angola, and good
results are anticipated, owing to the fact that Ceara
rubber grows well in a drier climate and at a higher
elevation than Hevea.

Biffen, who visited the North East coast of Brazil
in 1897, found large plantations already being opened
in the Ceara district, at elevations up to 3500 feet.
No recent reports regarding the development of these
plantations are available. The methods of collecting the
latex and preparing the rubber on plantations in Brazil
appear to be similar to those applied to the wild trees.
Tapping is generally carried out during the dry season
by slicing the bark with a knife.

The Ceara rubber plant grows readily from either
seeds or cuttings, but in order to ensure immediate
germination of the seeds it is necessary either to file
through the tip of the hard shell or to steep the seeds
for some time in warm water. The early growth of the
trees is very rapid, and it is often possible to begin
tapping earlier than in the case of Hevea. Close
planting is generally recommended, but this seems to be
a mistake. Trees have been planted at distances of

202 RUBBER AND

15 by 15 feet in more than one district in Ceylon, and
growth has been very rapid for the first two years.
At the end of this time the branches met and formed
a close cover, with the result that subsequent growth
was very slow.

The structure of the laticiferous system of Manihot
is closely similar to' that of Hevea. The Manihots are
the only other rubber-producing plants upon which
tapping can be carried out at an equally short interval,
and although the study of the subject has not been
carried so far as in the case of Hevea, the phenomenon
of wound-response seems to be closely similar in both.

Another advantage of Ceara rubber is that the plant
grows like a weed, so that trees which have been injured
in the course of tapping can be replaced with very little
trouble.

On plantations, the hard outer bark is generally
removed before tapping. Opinions differ as to whether
tapping should take place immediately after the outer
bark is removed or whether it should be delayed for
a longer or shorter period. In Africa the method of
tapping usually adopted is the primitive one of pricking
or stabbing with a blunt thin-bladed knife. The pricks
are made about an inch apart in a vertical series. Some-
times the bark is first rubbed over with a freshly cut
lime or lemon, in order that the latex may be coagulated
on the bark by the citric acid thus applied. The strips
of wet rubber formed upon the bark are collected by
rolling them up on sticks or small wooden rollers.

RUBBER PLANTING 203

When a thickness of about a quarter of an inch of
rubber has been obtained, the rolls are slit up so as to
form small sheets, which are subsequently washed and
dried.

The method of alternate paring and pricking recom-
mended in Hawaii has been found to cause considerable
damage to the trees in Ceylon. Paring on the herring-
bone system has sometimes been found to give good
results if not carried too far. If the paring extends over
only an inch of bark, and a space of an inch is then left
untapped before the next cut is made, the bark is
generally found to heal satisfactorily. Rather wide
shallow paring with a small gouge has given good
results on Ceylon estates, and has been followed by
perfect renewal. In many climates tapping can only
take place during dry intervals in the wet season, since
the trees drop their leaves during the dry season of the
year, and then yield little or no latex.

Coagulation takes place on the simple addition of
water. Very good samples of rubber, closely com-
parable with the best Hevea sheet in appearance, have
been prepared by diluting the latex with an equal bulk
of water and allowing it to stand until coagulation is
complete. The further processes involved are precisely
similar to those adopted in the preparation of Hevea
sheets or biscuits.

A process which should be rigidly avoided is the
mixing of the latices of Manihot and Hevea on estates
where both products are cultivated. Such mixture

204 RUBBER AND

leads to rapid coagulation without reagents, and to the
production of a rubber which is excellent in appear-
ance. Rubber of this kind is not, however, desired by
manufacturers, and the mixed character of the sample
is easily detected by experts. Manihot rubber requires
slightly different treatment in manufacture from the
produce of Hevea, and the mixed product is therefore
unsatisfactory.

The yields from young trees appear to be similar to
those from Hevea ; in subsequent years, however, the
increase in yield is not so great. In Nyassaland in 1910
four hundred four-year-old trees are said to have yielded
an ounce of dry rubber apiece from only two tappings,
and the cost of collection was only ^d. per Ib. In
this case the tapping consisted of making vertical rows
of pricks. At Peradeniya, Ceylon, experiments in paring
were carried out on trees only three and a half years old
at the beginning of the experiment, planted at the rate
of 200 to the acre. About four ounces of rubber per
tree were obtained in a year by 70 tappings. A yield
of nearly 50 Ibs. per acre was thus obtained at an earlier
age than that at which a similar amount of rubber could
safely be extracted from Hevea trees. The cost of pro-
duction, however, was hign.

Among other species of Manihot, M. dichotoma was
introduced into Ceylon in 1908. So far, none of the
new species have succeeded so well as Manihot
Glaziovii. The growth of the trees and the thickness
of bark were poorer at equal ages, and in the few

RUBBER PLANTING 205

experiments made the yield of latex was less. Manihot
dichotoma also suffered severely from the effects of wind
of no great force ; the trees were uprooted and branches
were split off in every direction.

Funtumia.

Funtumia elastica and its cultivation in Africa have
been made the exclusive subjects of a recent book by
C. Christy (The African Rubber Industry and Funtumia
elastica). From this work the few remarks here given
are partly summarised, and for fuller information refer-
ence may be made to the original source.

Some description of the species itself was given
in Chapter II of the present work. The seeds retain
their vitality well. They are very small, with a plume
of long silky hairs, and one ounce of seed is sufficient
for 20 square yards of seed bed. As germination at
even distances cannot be guaranteed, the seedlings may
with advantage be transplanted to a second seed bed
prior to planting out in the field. The further operations
of planting and cultivation are similar to those adopted
in the case of Hevea.

Very close planting is recommended, to be followed
by subsequent thinning. Close planting is said to be
necessary in order to obtain straight clean stems, to
obliterate lower branches which would interfere with
tapping, and in order to minimise the cost of weeding.
The thinning subsequently undertaken gradually leads

206 RUBBER AND

to a distance of 1 2 by 1 2 or 15 by 1 5 feet at six or seven
years of age. The trees are deep rooting ; consequently
manuring and cultivation have less effect upon growth
and yields than in the case of Hevea. A fair yield is
obtained from the sixth year onward. The average
growth in plantations is said to be of the same order as
that of Hevea, the increase in girth being from three to
four inches per annum.

As in the case of Castilloa, the trees can only be
tapped two or three times in a year, and great care has
to be exercised in order to avoid damage to the bark.
The method of tapping recommended by Christy is
by cutting shallow conducting grooves on a half-spiral
system. The slanting grooves are then to be pricked
with a thin-bladed spur pricker. Eight inches is
regarded as the best distance between the lateral
channels.

The trees are first tapped during the sixth year.
They are then tapped twice a year until they are eight
years old, and afterwards three times a year. The later
cuts are made about two inches above the old, and a
fresh vertical channel is made at each tapping. On old
trees the tapping may be carried to a height of 30 feet.

In a particular series of experiments, about five
ounces of dry rubber per tree was obtained by tapping
to a height of 30 feet on the double half-spiral system.
The average girth of the trees concerned was 28 inches.
Christy gives the following estimates of the average
annual yield per tree under plantation conditions.

RUBBER PLANTING 207

Age, years 5678 9 10

Dry rubber, ounces ...3 4 5 9 12 15

Coagulation is effected by simple dilution with water
or by the use of various reagents, amongst which tannic
acid, formalin and hydrofluoric acid are said to be
specially effective. The fresh latex is neutral in reaction
or very slightly acid, and acetic acid alone does not
produce coagulation. Centrifugal machines are also
useless, probably on account of the very small size of
the latex globules. The physical properties of the
rubber are found to vary considerably, according to the
nature of the chemical reagent employed.

Christy regards Funtumia as better suited than
Hevea for growth in African plantations. It is less
liable to the attacks of insect pests, and is much cheaper
to cultivate. It is also considerably cheaper to tap,
owing to the relatively large yields obtained at a single
tapping. Plantations have already been opened on an
extensive scale in Kamarun, and the cultivation is under
trial in Southern Nigeria and in other parts of British
West Africa.

The introduction of Funtumia into countries outside
Africa has not generally been attended with much
success, for in other climates the plant appears to
suffer widely from the attacks of insects. At Pera-
deniya the growth of the trees was found to be very
slow, largely owing to the depredations of a leaf-rolling
caterpillar, which led annually to the complete defoliation
of every branch.

2o8 RUBBER AND

Ficus elastica.

Sir Daniel Morris, in his Cantor Lectures, states that
"In 1873 tne Government of Bengal decided to start
regular plantations of Ficus elastica in Assam. The
order, issued in 1873, was repeated in 1876, and has
been acted upon with slight interruption until the
present time." In 1884 nearly 900 acres had been
planted in the Charduar district, and in the same year
directions were issued that the plantations should be
increased by 200 acres annually. It is said to be well
known that although the trees grow vigorously in
situations remote from the hills, the yields of rubber
are then almost negligible. It appears, however, that
even in its native hills the yields of the Assam india-
rubber tree are very small from a planter's point of view.
Thus in 1896 the Inspector General of Forests, H. C.
Hill, was glad to estimate a yield of a maund (about
80 Ibs.) per acre at an age of 50 years.

Ficus elastica has been widely planted in Java in
more recent years, but here again no better yields
appear to be obtained. Berkhout estimated 17 Ibs. of
dry rubber per acre in the eighth year from planting,
26 Ibs. in the tenth year, and 70 Ibs. an acre in the
twentieth year. Such yields render the trees almost
useless for plantation purposes, and in many parts of
the Dutch East Indies where they have been planted
they are already being cut down to make way for
Hevea.

RUBBER PLANTING 209

Another disadvantage of Ficus elastica is the very
rapid spontaneous coagulation of the latex, which makes
it impossible to collect and treat the latex by ordinary
methods.

Other species.

The above comprise all the species which have been
used at all extensively in plantations proper. The
method of replanting in the forests in which the wild
rubber plants have been partly destroyed is being
adopted in several countries, notably in Brazil and in
the Mabira forest of Central Africa. Rubber vines were
extensively planted some years ago in the Congo by the
orders of the Belgian Government. This method was
recently given up in favour of Funtumia plantations,
and still more recently there has been a tendency
to abandon Funtumia in favour of Hevea. On the
whole, it seems probable that in the future the world's
supply of rubber will depend more and more upon the
plantations of Plevea, including those established or
about to be established in Brazil.

CHAPTER X

THE CHEMISTRY OF INDIA-RUBBER

THE chemical composition and behaviour of india-
rubber are among the most difficult problems with
which the organic chemist is confronted. The nature
of these problems can only be indicated here in the
barest outline. For further information the works of
Weber and of Schidrowitz should be consulted. The
latter gives references to the original chemical papers
down to the end of 1910.

Technically pure rubber consists of crude com-
mercial rubber which has been thoroughly washed and
dried in vacuo. Much of the rubber produced on
plantations is therefore already practically in this
condition. The difficulties which stand in the way of
the further study of this substance may be stated in
the words of Weber : — " These difficulties are physical
rather than chemical, that is to say they do not so
much consist in the functional complexity of india-
rubber as in the circumstance that these molecules
are only known with the colloidal state superimposed
upon them."

RUBBER AND RUBBER PLANTING 211

Properties of Colloids.

A colloid may be defined as a substance which forms
a jelly-like solution, incapable of passing through a
membrane of parchment or similar material. Colloids
are thus contrasted with crystalloids which are able
in solution to pass through colloidal membranes. A
colloid does not crystallize, and has no definite melting
point ; in fact, the physical changes induced in it by
heat or by solvents are perfectly continuous so long
as the chemical molecule of the substance remains
intact. The isolation of a particular colloid from a
mixture containing other colloids offers great technical
difficulties, and such a substance is exceedingly difficult
to obtain in a chemically pure condition. All the
ordinary chemical tests of identity are baffled by the
consistency of such a material. The colloidal condition
is believed to be generally associated with the existence
of a very large chemical molecule.

Composition of technically pure Rubber.

Technically pure rubber is by no means pure in
the chemical sense. The chief impurities present are
various resinous and allied bodies, which can be
removed more or less completely by prolonged extrac-
tion with boiling acetone. The amount of the resins
and oily bodies extracted in this way varies from
I per cent, upwards, according to the origin of the

14—2

212 RUBBER AND

particular sample. Proteins and other nitrogenous
bodies are also invariably present in varying amounts,
and there is always a certain amount of ash remaining
on ignition. After the various impurities have been
determined as accurately as possible, the weight of
these is deducted from the original total weight, and
the residue is regarded as representing the amount of
pure caoutchouc present. The approximate compo-
sition of biscuit rubber prepared from the latex of old
Hevea trees at Henaratgoda was as follows : —

Resin, etc 2 per cent.

Proteins, etc i „

Ash 0-3 „

Rubber 96 „

Physical Properties.

In the highest attainable state of chemical purity,
india-rubber is a practically colourless and odourless
substance, possessing a specific gravity of approximately
0*911. It is insoluble in water, but is capable of
absorbing about 25 per cent, of its own weight of
water on prolonged immersion. Rubber is a bad
conductor both of heat and of electricity. Some of
its most important technical uses are dependent upon
the last named property. In so-called rubber solvents
the rubber swells into a jelly which finally " runs "
when a sufficient amount of the solvent is added. In
this way about 15 parts of rubber are soluble in 100
parts of benzene, and smaller amounts in turpentine,

RUBBER PLANTING 213

petrol, chloroform, carbon bisulphide and other solvents.
The rubber is more easily taken up by the solvent
after it has been mechanically kneaded in the rolling
or masticating machines, than in the untreated condition.
Weber considered that all these solutions should more
properly be regarded as solutions of the so-called
solvent in the india-rubber.

The mechanical strength of rubber which has once
been dissolved is greatly inferior to that of the crude
rubber. For this reason cut sheet rubber is superior
for many purposes to sheet which has been "spread"
from a solution. This fact renders it doubtful whether
synthetic rubber can ever be made equal in physical
properties to natural rubber. The mechanical kneading
to which raw rubber is subjected in the course of
manufacture has also a marked effect upon its physical
properties.

The value of rubber for many purposes depends
largely upon its chemical indifference, i.e. upon its want
of power to enter into combination with many other
chemical substances. Raw rubber undergoes slow
oxidation on exposure to the air, and it enters rapidly
into combination with ozone. Dilute acids and alkalies
have little or no effect upon it, but it is rapidly destroyed
by the action of strong sulphuric or nitric acid, or by
exposure to the action of chlorine, bromine or iodine.
The only compounds of rubber which have been at all
closely studied are those with sulphur, with the halogens
and with ozone.

2i4 RUBBER AND

On cooling raw rubber to the freezing point of water
the substance becomes hard and brittle, but recovers
its ordinary properties when restored to the normal
temperature. At warm summer temperatures the
elasticity of the rubber is increased, but on further
raising the temperature the rubber becomes softer and
more extensible. If the heating is not carried too far,
the normal properties of the rubber are recovered on
cooling. Heated still further the rubber becomes soft
and sticky, becoming actually liquid at some point
above 200° C. If cooled again from such a temperature
the normal elasticity of the rubber is no longer
recovered. At still higher temperatures the rubber
undergoes dry distillation with destruction of the
molecule.

Destructive Distillation. — Synthesis.

The destructive distillation of india-rubber gives rise
to isoprene C5H8, and to other bodies of the formula
(C5H8)n. Isoprene is also the most important step in
the synthesis of rubber, for which a number of com-
mercial processes have recently been patented. Tilden,
many years ago, obtained true rubber from isoprene
which had been prepared by passing the vapour of
turpentine through heated tubes. The rubber appeared
spontaneously in the isoprene which had been kept for
some years in a closed bottle, and was also produced
more rapidly in small quantities by the action of

RUBBER PLANTING 215

hydrochloric acid. The last named method of prepara-
tion confirmed a previous discovery by Bouchardet.

The production of rubber from isoprene is a process
of polymerisation , that is to say the union of a number
of molecules each possessing the same empyrical formula^
i.e. containing the same relative number of carbon and
hydrogen atoms. Analysis has shown that rubber con-
tains carbon and hydrogen in the same proportions
as exist in isoprene and turpentine. A study of the
compounds of rubber, particularly those with ozone, has
led Harries to represent the polymerisation of isoprene
in the following manner:

/H,

_ r*

II II « " \ ^CH

H— C C— CH3 ^C C '

I + I =1 8

CH3-C C-H "c <•

\

H2=C C=H,

The actual molecule of rubber is probably a polymer
of the substance whose constitution is represented
above, and may consist of a number of similar eight-
ring molecules linked together. The empyrical formula
of rubber is thus C10H16, which is identical with those of
turpentine and gutta-percha. The molecule of the latter
is probably even more complex than that of rubber, but
may possibly be a higher polymer of the same series.
It should be observed that the account here given of

216 RUBBER AND

the constitution of the rubber molecule only represents
one of the most recent theories. The problem of the
structure of this molecule cannot yet be regarded as
finally settled.

In some of the modern processes which have been
proposed for the manufacture of synthetic rubber on
a commercial scale, isoprene is prepared from fusel oil,
obtained from starch by special methods of fermenta-
tion ; and polymerisation is effected by the action of
metallic sodium. Various other substances have also
been synthesised, which, though differing in composition,
appear to possess a similar molecular structure to india-
rubber. The physical properties of some of these bodies
are closely similar to those of rubber, and their use has
been proposed commercially for similar purposes. So
far, none of these substances have been placed upon the
market in appreciable quantities, and the reports of the
cheap production of synthetic rubber have not carried
with them a fall in the value of plantation shares.

Vulcanisation.

The molecule of rubber is unsaturated, and is able
to enter into direct combination with different elements.
This fact is expressed in its constitutional formula by
the presence of double links between two pairs of
carbon atoms in the ring. Among the addition pro-
ducts of rubber, those with sulphur possess the greatest
technical importance. Rubber combined with sulphur

RUBBER PLANTING 217

is said to be vulcanised. We have already referred in
Chapter I to the remarkable properties of resistance
and durability possessed by vulcanised rubber.

Rubber is vulcanised by two entirely different
processes. In hot vulcanisation the rubber is directly
combined with sulphur under the influence of heat. In
cold vulcanisation, rubber is combined, without heating,
with chloride of sulphur dissolved in benzene or other
solvent. The molecule of rubber vulcanised by the
second method contains chlorine as well as sulphur.

Vulcanisation with hot sulphur was discovered by
Nelson Goodyear in 1839. At the melting point of
sulphur there is little or no action. Combination begins
at about I2O°C., and the temperatures used in practice
range from I25°C. upwards. According to the amount
of sulphur employed, the time of action and the
temperature, the final product ranges in character from
soft elastic to hard vulcanite.

Weber considered that the process of vulcanisation
was one of definite chemical combination. He believed
that a series of sulphides of rubber were formed ranging
from (C10H16)2oS2 to the final product vulcanite, to which
he attributed the formula C10H16S2. This opinion, which
has been subjected to severe criticism, appears to be
confirmed by the results of the most recent researches.
The process is a reversible one, and the vulcanised
rubber apparently always contains a certain amount
of uncombined rubber and a certain amount of free
sulphur. As a result, goods which have only been

2i8 RUBBER AND

partially vulcanised become more fully vulcanised on
keeping. It is therefore the practice to vulcanise the
majority of goods rather less completely than is finally
required.

Some recent writers still regard the process of
vulcanisation as one of adsorption. That is to say
they look upon the vulcanised rubber as existing in
a condition of physical mixture rather than in one of
true chemical combination. As previously stated, the
whole problem is one of extreme difficulty, and we are
perhaps still far from a final solution.

The physical condition of the rubber has a marked
influence upon the final product, and the same sample
of raw rubber, if differently worked before vulcanisa-
tion, requires to be vulcanised with a different quantity
of sulphur and to a different extent in order to produce
the same final result. After long continued kneading
and mastication more sulphur is required in order to
bring the vulcanised rubber to the same condition of
physical consistency.

The process of cold vulcanisation with sulphur
monochloride was discovered by Parkes in 1848. The
action is exceedingly vigorous. Dilute solutions are
therefore employed, and the period of contact is short.
The solvent almost universally employed is carbon
bisulphide.

The action of sulphur monochloride on rubber, like
that of sulphur, is an addition and not a substitution
process. This is proved by the fact that no sulphuretted

RUBBER PLANTING 219

hydrogen is emitted during the process of combination.
The action probably gives rise to a series of addition-
products parallel with those arising during simple
vulcanisation with sulphur. The series would then
begin with (Q»Hw)bSiCls and end with C10H16S2C13.
The fact that the addition of large amounts of the
pure solvent leads to the extraction of S2C12 from
the vulcanised rubber is equally well explained on
the hypothesis of a reversible chemical action as it is
on the adsorption hypothesis.

CHAPTER XI

THE MANUFACTURE OF RUBBER GOODS

THE principal processes employed in a rubber
factory begin with the washing and drying of the crude
commercial samples, which require thorough cleansing
in order that technically pure rubber may be obtained.
From this point two series of operations diverge,
which may be distinguished as wet and dry processes
respectively. In the former the rubber is dissolved
in naphtha or benzene, and is then deposited from the
solution in moulds or on cloth. The articles so formed
are subsequently vulcanised, often by the cold process,
i.e. the action of sulphur monochloride. The bulk of
the larger and more solid goods are manufactured by
a dry process. In this the rubber is first masticated
or kneaded, in order to bring it into a suitable condition
for the next operation, that of mixing, in which various
filling and diluting materials are intimately distributed
through the substance of the rubber, together with the
sulphur required for vulcanisation. The mixed rubber
is then moulded or forced or built up with layers of

RUBBER AND RUBBER PLANTING 221

canvas into the various articles which are being made
in the factory. Vulcanisation is subsequently carried
out by steam heat in moulds or presses or closed
chambers. Certain other articles again are cut out of
rubber already vulcanised.

Washing.

It has already been pointed out that in dealing with
the pure samples of rubber now produced on estates,
the preliminary cleansing operations, necessary in the
case of all ordinary commercial samples, will probably
be omitted from the series of manufacturing processes
in the rubber factories of the future. The washing
machines used in factories are generally similar to those
employed upon estates, but are usually larger and more
powerful. They are generally driven from shafting
through powerful clutches, and special arrangements
are often introduced for throwing the machinery auto-
matically out of gear in case of accident, for example
when large stones or other bodies liable to cause damage
are encountered. Prior to the actual process of washing,
large commercial blocks are softened by soaking in hot
water, and are sliced into smaller pieces by special
machines, either before or after the softening process.
A series of washing machines is usually employed, and
the rollers through which the rubber first passes have
coarser grooves and are set further apart than the later
members of the series. The arrangement thus resembles

222 RUBBER AND

to some extent the series of rollers in a modern flour
mill, although the processes of rubber washing and flour
milling have little other resemblance. By passing
repeatedly through the washing rollers under a stream
of water, the impurities present in most kinds of com-
mercial rubber are gradually washed away, and the
rubber finally emerges in the form of a thin crepe
convenient for drying. The rubber itself undergoes
much tearing and stretching during the process, and it
is important that this mechanical action should not be
carried further than is absolutely necessary in order to
ensure a sufficient degree of purity, since the " nerve "
of the rubber is largely destroyed by the forcible treat-
ment involved.

Drying.

The so-called "nerve" lost in washing is partly
recovered during the slow process of drying, which is
effected by hanging the strips of rubber in large
chambers exposed to a current of dry air. The drying
of the washed rubber takes place more readily than
in the case of rubber freshly prepared from latex, since
the moisture is not so closely incorporated in the
substance of the rubber. On the other hand many
commercial rubbers, for example hard Para, contain a
considerable proportion of the original moisture derived
from the latex. When this moisture in addition to the
water introduced during washing has to be removed,
the drying process takes considerably longer.

RUBBER PLANTING 223

Vacuum driers are also under trial in certain
factories, but it is said that rubber dried in this way
does not recover its " nerve " so completely as it would
if the slower process of air drying were adopted.
Drying machines of this type are, however, frequently
employed for desiccating the materials used for mixing
with the rubber, thorough dryness being essential in the
latter process.

Mastication and Mixing.

Mastication is sometimes carried out in a machine
resembling a powerful churn or sausage machine. For
most purposes rollers are employed similar to or
identical with the mixing rollers. Mixing is always
preceded by a masticating process, introduced in order
to soften the rubber. The dried rubber is passed
repeatedly between a pair of hollow rollers, which can
either be heated internally by steam, or cooled by
passing cold water through the cavity. The rollers
revolve at different rates, and the distance between
them is adjustable. The rollers are gradually brought
closer together until the soft rubber adheres to the
slower moving roller and passes round with it, being
subjected to a kneading process as it passes the second
roller, which revolves more rapidly. At the beginning
of the process the rollers are warmed, but later on
friction may give rise to so much heat that it is
necessary to pass cold water into the interior of the

224 RUBBER AND

rollers. The whole process thus calls for considerable
skill and judgment on the part of the operator in
regulating both the temperature and the action of the
machine.

After undergoing a certain amount of mastication
the rubber is judged to be ready for mixing. In the
mixing process, the sulphur required for vulcanisation
is incorporated with the rubber, together with other
substances known as fillers. The rubber is passed
repeatedly between the rollers and the sulphur, and
filling materials are gradually sprinkled over it in the
form of a fine powder. The process of rolling is then
continued until the fillers are evenly distributed through
the rubber, and the whole substance has become nearly
homogeneous.

Sulphur is introduced either in the form of flowers
of sulphur or as precipitated sulphur. Other substances
are used in the mixing for several definite purposes.
Thus various sulphides aid in the process of vulcanisa-
tion. These and other chemicals are also introduced
in order to impart definite qualities of toughness and
durability to the finished product. Among the most
important of these substances are zinc oxide, magnesia,
antimony sulphide and litharge (lead sulphide). Some
of these chemicals impart characteristic colours to the
rubber, whilst a further series of materials is used simply
for colouring. Thus red rubber may contain vermilion,
red lead or antimony sulphide ; whilst white or grey
rubbers usually contain zinc oxide, and black rubber

RUBBER PLANTING 225

contains either litharge or some form of carbon black.
Finally, there are the filling materials which are intro-
duced in order to reduce the specific gravity of the
rubber or to lower the cost. Rubber is sold by weight,
and the materials used for toughening have mostly high
specific gravities. Substances of low specific weight
are therefore introduced in order to counteract the effect
of the heavy bodies. For this purpose whiting and
French chalk are largely employed. For cheapening,
a large variety of substances is used, foremost among
them being old vulcanised rubber in a more or less
reclaimed condition. Fatty oils undergo a kind of
vulcanisation with sulphur, and are used as cheapeners
in combination with reclaimed rubber. With low grades
of rubber such substances as leather waste and sawdust
may even be incorporated.

The further treatment of the mixed rubber varies
according to the kind of article which is to be manu-
factured. Very commonly it is treated in one of three
ways. It is either pressed into blocks, or rolled into
sheets, or moulded in what is known as a forcing
machine.

Preparation of Sheet Rubber.

A large proportion of rubber articles are manu-
factured from sheet rubber. The highest class of sheet
rubber is cut from block, but this method is less used
than formerly, on account of the increased perfection of
other methods. For making "cut sheet," the rubber,

226 RUBBER AND

after masticating and mixing, is pressed into a solid
block. The block is then frozen hard, an operation
which takes a long time owing to the low conductivity
of rubber for heat. After freezing, the block is cut into
sheets by one of two methods. In the older method
the block of rubber was sliced horizontally, being raised,
after the removal of each sheet, by an amount equal to
the thickness of the sheet. In the second method a
cylindrical block is made to rotate against the knife
blade, which thus slices off a continuous sheet. The
knife is kept wet during the process, and special
methods of sharpening and setting have to be
adopted.

Raised sheet is prepared by spreading rubber in
solution over cloth, in a very thin film. A series of
such films are spread over the cloth, the solvent being
allowed to evaporate between each spreading. Finally
the cloth is detached from the sheet of rubber thus
produced. A similar process is employed in water-
proofing, in which a thin layer of rubber is permanently
attached to the surface of the cloth. Sometimes two
layers of cloth are united by a thin layer of rubber
placed between them. It was for waterproofing that
rubber in solution was first employed. Sheet rubber
prepared on cloth in this way carries the grain of the
cloth upon its surface. Sheet having a perfectly
smooth surface can also be prepared from solution by
spreading the dissolved rubber over the surface of a
plate of glass.

RUBBER PLANTING 227

Calendering.

At the present day by far the largest proportion
of sheet rubber is prepared in machines known as
calenders. Indeed, the calenders are among the most
important machines in modern rubber factories. A
calender consists of a series of heavy rollers revolving
alternately in opposite directions. A common type
has three rollers arranged one above the other. The
rubber mixture is fed between the upper and middle
rollers. The sheet thus formed, varying in thickness
according to the distance at which the rollers are set,
adheres to the middle roller and passes back between
the middle and lower rollers. For packing the sheet
thus obtained, the following method is adopted. A
sheet of cloth is unwound from a drum on one side
of the machine. The cloth passes between the middle
and lower rollers, and is rolled up together with the
rubber sheet on the opposite side of the machine, If it
is desired to make the rubber adhere closely to the
cloth, the middle and lower rollers are made to revolve
at different rates of speed, and the friction thus caused
produces the desired adhesion. The rubber is then said
to be " frictioned " on to the cloth. Frictioned sheet
is used in the manufacture of a large variety of articles
in which alternate layers of cloth and rubber have to be
incorporated.

228 RUBBER AND

Manufacture of Various Articles.

A large variety of articles are made directly from
sheet rubber. The highest class of cut sheet rubber is
used in the manufacture of such articles as tobacco
pouches. Permanent joints can be made by simply
pressing together the cleanly cut edges of the sheet.
In order to prevent adhesion at other points, French
chalk is dusted over the surface. If lower grade sheet
is used, it may be necessary to moisten the edges with
solvent or with rubber solution in order to make a
permanent joint.

Block rubber is reconstructed from sheet for the
manufacture of such articles as railway buffers. The
sheet is rolled up into a cylinder and firmly pressed
together. Greater strength is thus obtained than by
simply blocking the mixed rubber. The nature of the
increased strength may be understood from the analogy
of heavy guns wound from wire, which are much
stronger than the old fashioned guns cast in one
piece.

Large tubes, such as the inner tubes for motor tyres,
are made by rolling the sheet rubber round an internal
mould known as a mandrel. The edges of the sheet
are joined together with solution. The ends of the tube
are cemented up after vulcanisation and removal from
the mandrel. The removal of the tube is effected by
the aid of compressed air. Smaller tubes of a simple

RUBBER PLANTING 229

kind, and such articles as solid rubber tyres, are made
by "squirting" the rubber mixture through a die by
means of a forcing machine. Such a machine consists
of a large screw working inside a cylinder, and so
forcing the rubber forward after it has been fed in
through a hopper at the top of the machine. In
making tubes a rod or mandrel is made to pass through
the centre of the screw and of the die, and the rubber
is forced round the mandrel, which is moved forward
at a suitable rate. The mandrel may be first coated
with canvas and the rubber forced over it. Another
layer of canvas can then be applied, and the forcing
process repeated, until a large tube has been built up
of alternate layers of canvas and rubber. Other tubes
may be built up by hand on a mandrel with alternate
layers of sheet rubber and cloth. The covers of electric
cables are similarly constructed, or they may be wound
with thin ribbons of rubber in a special machine. A
large variety of other articles are prepared by moulding
or pressing the rubber whilst in the plastic condition.

In making india-rubber balls and other hollow
objects, a small blob of india-rubber containing no
sulphur is placed against one side internally. When
the ball cools after vulcanisation the walls collapse
The ball is then inflated through a fine-pointed syringe
pushed through the lump of soft rubber. When the
syringe is withdrawn the hole is closed airtight by the
unvulcanised rubber, and the inflated condition is thus
preserved.

230 RUBBER AND

Various other simple articles are cut from rubber
which has already been vulcanised. Rubber rings, for
example, are sliced off the ends of vulcanised tubes.

Rubber Solution.

A large variety of objects is manufactured by
dipping prepared fabrics in rubber solution. The sol-
vents chiefly employed are benzene and mineral
naphtha. The rubber is rendered more readily soluble
by undergoing previous mastication. Rubber shoes
and galoshes are dipped by dozens at a time in tanks
of solution and afterwards allowed to. dry. Teats for
feeding bottles are made by dipping glass moulds
repeatedly in clear solution, with intervals for drying.
Some of the smaller articles prepared in this way are
vulcanised by the cold process, but for larger objects
the sulphur required for vulcanisation is incorporated
in the solution. For repairing motor tyres a quick-
vulcanising mixture is employed, in order that the rest
of the tyre may not be damaged by the heat required
for vulcanising the mended area.

Vulcanisation.

H. C. Pearson has pointed out that the natives of
some parts of the Amazon districts are accustomed
to mix sulphur with the latex of Hevea before employing
it for waterproofing. True combination between the
rubber and the sulphur, however, apparently only occurs

RUBBER PLANTING 231

at a high temperature. We have already distinguished
in the last chapter between hot and cold vulcanisation.
Under hot vulcanisation again two processes may be
separately considered. Of these, the more important is
the dry process originally patented by Goodyear. In
this process the proper amount of sulphur is incorporated
with the rubber in the mixing rollers before the articles
are made up, and vulcanisation is effected by heating
either directly in steam under pressure or in steam-
jacketed chambers, or in hydraulic presses heated by
steam in various ways.

Hancock's wet process, on the other hand, is chiefly
of historical interest. In this process articles made of
sheet rubber, without any previous admixture of sulphur,
are immersed in molten sulphur for a certain time and
at a certain temperature.

Finally, in the cold process, patented by Parkes in
1848, the articles are immersed in a solution of chloride
of sulphur, in carbon bisulphide, or in benzene. This
process is exceedingly rapid, and can only be applied to
articles of very thin sheet.

The Dry Process.

The chambers used for vulcanising by the dry
process are often of very large size. They may take
the form of great iron tunnels, into which the articles
to be vulcanised are run on rails. Hose pipes are often
vulcanised in lengths of 60 feet or more. The rubber

232 RUBBER AND

becomes soft and plastic at the temperature employed,
and must therefore be supported in order to preserve
its shape. Powdered French chalk is largely employed
as a bed for the rubber articles to lie on. Closed objects
such as balls, india-rubber dolls and other toys, are
vulcanised in moulds, and before the cavity of the
rubber is closed up some substance is introduced which
will volatilise at the temperature of vulcanisation, and
so press the object firmly against the mould. The
outer covers of motor tyres are vulcanised in heavy
presses, in order that their substance may be firmly
compacted during the process. The most complicated
of all vulcanising machines is the autoclave press, which
consists of a hydraulic press completely enclosed in a
steam pressure chamber. In this way the difficulties of
obtaining an even temperature in a press heated by
steam pipes are overcome. Vulcanisation by steam is
generally carried out at a pressure of three to four
atmospheres (45 to 60 Ibs. per square inch) corre-
sponding to a temperature of I34°C. to 144° C. The
temperature and pressure are first raised gradually,
and afterwards kept high for three or four hours. Self-
recording thermometers and pressure gauges are fitted
to the apparatus in order that the process may be kept
under complete control. The time required for vulcani-
sation varies according to the source of the rubber,
being shortest in the case of Hevea rubber. The
previous treatment of the rubber also affects the
process. Thick articles naturally require to be heated

RUBBER PLANTING 233

for a longer period than thin ones. The proportion of
sulphur added to the rubber varies according to the
nature of the articles to be manufactured. For ordinary
goods the quantity is- about 7 to 10 per cent, of the
amount of rubber.

Bath Process.

In Hancock's bath process, which is comparatively
little used, small objects are immersed in molten sulphur
for a period of two or three hours at a temperature
of I3O°C. to I35°C. Test pieces of rubber, of similar
thickness and composition to the articles to be vul-
canised, are placed in the same bath and removed at
intervals. From the appearance of these the operator
is able to judge when the process of vulcanisation is
complete.

Cold Process.

The cold process, discovered by Parkes, can only be
used for vulcanising very thin sheet. This is due to the
extreme rapidity of the process, which is such that if it
were applied to thick rubber, the surface of the object
would be converted into vulcanite before the interior
was properly vulcanised. The reagent employed is
sulphur monochloride, prepared by passing dry chlorine
over heated sulphur. This substance is very active
chemically, and is decomposed by water. As a solvent,
carbon bisulphide is almost universally adopted. Carbon

234 RUBBER AND

bisulphide is exceedingly poisonous and inflammable,
but no other solvent has been found to give equally
good results. The strength of the solution used is
generally about 2^ per cent. The sheet rubber, which
must first be very thoroughly dried, is immersed in
the solution for three minutes or less, according to its
thickness.

Whatever the method of vulcanisation employed,
there is always a certain amount of after effect, owing
to the prolonged slow action of the residual rubber.
Articles are therefore almost always rather less perfectly
vulcanised than their final condition requires. The
goods afterwards improve to some extent by keeping.
In the case of articles in which a high degree of
permanent elasticity is required, the excess of sulphur
must be removed by boiling in caustic soda, followed
by a thorough washing in water in order to remove the
alkali. This process is necessary, for example, in the
manufacture of elastic thread, which is cut from vulcan-
ised spread sheet and afterwards freed from sulphur in
the manner described.

Reclaimed Rubber.

During recent years the scarcity and high price of
fresh rubber has led to the use of enormous quantities
of old rubber, reclaimed in various ways, either in
combination with fresh rubber or alone. Old rubber
may be simply ground to powder and employed as

RUBBER PLANTING 235

a filling material with fresh rubber, but the bulk of the
reclaimed rubber used in manufacture goes through a
series of complicated processes. The discarded rubber
goods used for making reclaim, whether they be old
rubber shoes or old motor tyres, usually contain a con-
siderable quantity of cotton fibre. In order to remove
this fibre the rubber is boiled with dilute sulphuric acid,
and the cotton thus disintegrated can then be got rid of
by grinding, combined with the use of an air blast. The
acid process is generally followed by an alkali process,
in which the free sulphur is removed by boiling with
caustic soda. The residual rubber is then heated with
resin-oil, and can afterwards be manipulated more or
less like ordinary unvulcanised rubber. The reclaimed
rubber contains all the mineral substances originally
added, so that little further mixing is required if a
similar class of goods is to be remanufactured.

In addition to the methods described above, it is
claimed that processes have already been perfected by
which the sulphur of vulcanisation can be more or less
completely removed from the old rubber. Schidrowitz
states that other processes have been recently introduced
by which " particles of vulcanised rubber in the shape
of dust or flakes can by pressure and heat be moulded
to a homogeneous mass, which, on cooling, is to all
intents and purposes indistinguishable from an ordinary
moulded article."

236 RUBBER AND

Vulcanite.

The manufacture of vulcanite resembles in principle
that of ordinary rubber goods at all stages, except that
a larger proportion of sulphur is added in the mixing
and that vulcanisation is carried out for a longer period
and at a higher temperature. As we proceed to stages
of vulcanisation beyond that for ordinary hard vulcan-
ised rubber, we pass through the tough and springy
condition of the substance employed as artificial
whalebone, and finally arrive at the hard and brittle
state of the vulcanite or ebonite employed for making
fountain pens and the mouthpieces of pipes — to name
only two of a large variety of uses. In making whale-
bone-substitute the amount of sulphur added to the
rubber is from 12 to 14 per cent.; for the harder
ebonite from 24 to 35 per cent, is required. Vulcani-
sation is carried out either for a prolonged period —
8 to 12 hours — at a comparatively low temperature —
about I35°C, or for a shorter time at a higher tempera-
ture.

The Testing of Rubber Goods.

A number of ingenious devices are employed in
determining the quality of rubber goods as well as that
of raw rubber. The principal tests to which manu-
factured rubber is subjected are those for abrasion and
for stretching. In abrasion tests the sample is brought

RUBBER PLANTING 237

in contact with a rotating wheel of definite composition
for a certain time and with a certain pressure, and the
loss in weight of the rubber is afterwards determined.
For stretching tests special machines are used in order
to cut perfect rings from sheet of uniform thickness.
The ring is tested by passing it round two rollers, which
rotate at an even speed whilst they are gradually moved
further and further apart by a stretching force, the
amount of which is recorded upon a dial. The force
required in order to produce a certain elongation, or to
break the ring, may thus be determined.

CONCLUSION.

We have now followed the fortunes of rubber from
the wild territories of the Amazon to the plantation,
and from the plantation to the factory. Here we may
take leave of it, conscious that the last word on the
subject is far from being said. In fact, we shall pro-
bably be safe in asserting that the future history of the
rubber industry will be at least as interesting and
eventful as its past history. At every stage of its
career, rubber still presents problems which the planter
and the manufacturer must join hands in solving, with
the help of their scientific advisers.

INDEX

Acre, 21

Acreage under rubber, 12
Africa, Central and East, plantation
industry in, 1 1

West, 33
African rubber, 30 et seq.

largely exterminated, 30

new plantations of, 32
Agricultural machinery, 99
Alstonia, 36

plumosa, 36
Amazon region, 17

foodstuffs in, 23

rubber industry, economic as-
pects of, 21
Amazonas, 21

American species of rubber, 17 etseq.
Angle of cut, 145
Angola, 33

rubber planting in, n
Animal pests of Hevea, 179
Asiatic rubbers, 34
Assam, 34, 208

Balls, india-rubber, 229
Bamber, M. Kelway, 56

pricking method, 134
Bark, effects of wounding the, 47

renewal of, 49

ringing the, 47, 48
Basal system of tapping, 139
Bath process, Hancock's, 233
Biffen, centrifugal method of separ-
ation, 159
Biscuit rubber, 154

approximate composition of,

Block rubber, 164, 167

Bordeaux mixture, for Pink disease,

190

Boring insects, 52
Borneo, 36
Botanical sources of rubber, 16 et

seq.

Botryodiplodia theobromae, 191
Bouchardet, discovery by, 215
Bowman-Northway pricker, 132
Brain, Lewton, estimate by, 13
Brazil, collection of rubber in,

*9

labour in, 23

replanting wild rubber in, 209

transport in, 23

Brazilian Government, encourages
rubber planting, 12

legislation by, 22

premiums offered by, 23

special concessions by, 23
British India, wild rubbers from, 5
British West Africa, Funtumia in,

207

Brown root disease, 186
Burma, Ficus elastica in, 34

Hevea plants sent to, 7
Burrs, 192

Cacao, as intercrop, 114
Calendering, 227
Cambium, 41, 44, 48
Cambodia, 35
Canker, 187

of Hevea fruits, 189

remedy of, 188
Capital in rubber, 15

RUBBER AND RUBBER PLANTING 239

Carpodinus lanceolatus, 33
Castilloa, 8, 26, 197 et seq.

bark of, 27

in Central America, 198

in Ceylon, 199

in Jamaica, 200

in Mexico, 198, 200

in New Guinea, 200

in West Indies, 200

Markhamiana, 27

tapping of, 28, 199

wound response in, 59

yield from, 198
Caucho rubber, 26
Ceara, 24

at Peradeniya, 204

coagulation of, 203

difficulties in tapping, 25

growth of, 20 1

in Brazil, 201

in Ceylon, 200

in Hawaii, 203

in Nyassaland, 204

in Zanzibar, 201

seeds of, 25
"Ceara scrap," 25

tapping of, 24, 202

tapping difficulties, 200

yields from, 204
Centrifugal method, 159
Ceylon, Castilloa in, 199

draining in, 104

ffevea in, 7 et seq., 95

labour in, 123, 124

land tenure in, 97

nodules in, 193

plantation industry in, 10

plantation yields in, 152

planting distances in, 106

rate of growth in, 1 1 1

tools used in, 126

transport in, 97

wages in, 125

Chemistry of rubber, 210 et seq,
Christy, C., on Funtumia, 205
Clearing, 98

Clitandra henriquesiana, 33
Coagulation, 54, 153, 157 et seq.
Cochin China, 35

Cockerill, electrolytic method of

separation, 159
Coffee, as intercrop, 114
Coffee leaf fungus (Hemileia vasta-

trix), 177

Cold process, Parkes', 233
Collection of rubber in Brazil,

!9
Collins, James, 5

brings first seeds of Hevea, 6
Colloids, 2ii
Columbus, 3

Condamine, C. M. de la, 3
Congo, 33

rubber vines planted in, 209

wild rubbers from, 5
Cortex, 40

Cotton, as intercrop, 114
Cover crops, 112, 113
Crepe, 162, 163

pale, 164
Creping, 164
Cross, 5

brings Castilloa seeds, 6

introduces Ceara rubber to

Kew, 6

Crotalaria, 113
Cultivation, 115
Cut, angle of, 145

direction of, 146
Cuts, distance between, 146

Deep forking, 115
Die-back, 191

remedy for, 192
Diseases of Hevea roots, 183
Draining, 103

in Ceylon, 104

in Malaya, 104

on hillsides, 105
Drought, 112
Drying, \6ietseq., 222
Dry rubber, analysis of, 85

crop in Ibs., 73

yield of, 77

yields of, at Henaratgoda,
62

yields per acre, 64
Dust mulch, 113

240

RUBBER AND

Dutch East Indies, rubber cultiva-
tion in, 1 1
Dyera> 36

East and West Indies, suggested by
Hancock for rubber produc-
tion, 5
Economic aspects of Amazon rubber

industry, 21
Enzyme, 55
Epidemics, 177
Erythrina lithospcrma, 119
Estate expenses, 125

factory work on, 153
general sanitation of, 194
routine of, 129

Estimate, for planting 500 acres, 127
Estrade, 20
Excision methods of tapping, 59,

136
Exhibition, World's First Rubber, at

Peradeniya, 10

Exhibitions, in Rio de Janeiro, 23
Exports of rubber from East, 13
from Malaya, 13

Factory, cleanliness in, 156

lighting of estate, 155

machinery for estate, 155

site of, 154

work, on estate, 153
Federated Malay States, area of
rubber plantations in, n

draining in, 104

plantation industry in, 10, n
Ficus elastica, 34

in Assam, 208

in Java, 208

Sir Daniel Morris on, 208

tapping of, 35

yields from, 208
Ficus Vogelii, 33
Fiji, 36
Fitting, on food supplies of tree, 49

on tapping, 48
Fames semitostus, 183
Forsterionia fioribunda, 29

gracilis, 29
Fungus diseases, 182

Funtumia elastica (Kickxia afri-
cana), 27, 30, 197, 205 tt seq.
coagulation of, 207
laticiferous system of, 43
pests affecting, 207
planting of, 205
seeds of, 205
tapping of, 30, 206
wound response in, 59

Galoshes, 230

Gloeosporium alborubrum, 191

Gold Coast, wild rubber exported

from, 5

Goodyear, Nelson, discovers vul-
canisation, i, 217
Growth, rate of, in Ceylon, in

in Malaya, in
Guayule rubber (Parthenium ar-

gentatum), 29
processes of, 30
Guttering, 150

Half-herring-bone system, 137
Half-spiral system, 139
Hancock, Thomas, bath process,

233

employs rubber for waterproof-
ing, i
suggests cultivation of rubber,

5

Hancornia speciosa^ 28
Harries, on isoprene, 215
Harvesting operations, 128
Hawaii, Ceara in, 203
Hayti, 3
Henaratgoda, 7

experiments at, by the author,

yield from one tree, 66-67
Herring-bone system of tapping,

I33».i39

Hcvea brasiliensis, 4, 16, \*j et scq.
bark, minute anatomy of, 45
canker of fruits, 189
choice of situation and soil, 93
early experiments in Ceylon, 9
first seeds brought from Amer-
ica, 6

RUBBER PLANTING

241

Hevea brasiliensis, continued

flowers of, 19

fungus diseases of, 182

gross structure of bark, 44

in Ceylon, 8

irrigation in cultivation of, 105

latex, coagulation of 54

latex, composition of, 53, 54

latex vessels in, 43, 45

leaf-fall, 19

pests of, 176

planting operations, 93

plants arrive in Ceylon, 7

plants sent to Burma, Java,
Singapore and W. Indies, 7

plants sent to Mauritius, W.
Africa and Fiji, 7

repeated tapping of, 91

seeds of, 19

seeds, 122

tapping experiments in, 56

section of bark, 46

species of, 17

Spruceana, plants sent to Cey-
lon, 7

wound response in, 59

yields of rubber from one tree,

9

Hill, H. C., on Ficus elastica, 208
Holing and planting, 109
Hooker, Sir Joseph, 5
Hose-pipes, 231
Hymenochaete noxia, 184, 186

Incision, methods of, 59
India, rubber planting in, 1 1
India-rubber balls, 229

chemistry of, 210
Indigo, as intercrop, 114
Indigofera, 113

Insects, pests of Hevea, 180 et seq.
Intercrops, 108, \\^etseq.

cacao, 114

coffee, 114

cotton, 114

in Ceylon, 113

in Sumatra and Java, 114

indigo, 1 1 4

tea, 114

Irrigation, 103
Isoprene, 214 et seq.

Java, 7, 35

Ficus elastica in, 208 >

labour in, 122
Jelutong rubber, 36

export of, 37

Kamarun, Funtumia in, 207
Kerckhove, Van den, estimate by, 12
Kickxia africana, see Funtumia
elastica

Labour, in Brazil, 21

in Ceylon, 123, 124

in Java, 122

in Malaya, 123, 124

in S. India, 123

system of advances, 125
Lagos silk rubber (Funtumia elas-
tica), 30
Lagos, wild rubber exported from,

5
Land tenure, in Ceylon, 97

in other countries, 97
Landolpkia, climbing rubber, 17, 32

Dawei, 33

Jlorida, 33

Heudelotii, 33

Kirkii, 33

owariensis, 33
Latex, 38

bulk extracted in a year, 91

cleanliness in dealing with, 151

effect of tapping on, 82

effect of water supply on, 88

manufacture of, 69

movement of, 70

origin of, 68

percentage of rubber in, 83-84

physiology of, 56

production, physiology of, 38

protective function of, 52

seasonal variation in, 71, 84

seasonal variations in concen-
tration of, 84-85

smoking of, 165

transport of, 156

16

242

RUBBER AND

Latex, continued
tubes, 41, 42
vessels, 48

vessels, in Hevea, 43, 45
vessels, in Manihot^ 43
vessels, volume of, 67
yield at certain seasons, 92

Latices, mixing of, 204

Laticiferous system, 43, 44
in Funtumia, 42
in the seedling, 46, 47

Lettcaena glauca, 118

Lining and spacing, 106

Macadam's comb pricker, 133
Machinery, agricultural, 99, 1 1 5
Machines, cre'ping, 162

macerating, 162

sheeting, 161

Macintosh, Charles, and Co., i
Madagascar, 33

Malaya, estimated export of rubber
from, 13

labour in, 123, 124

plantation yields in, 152

planting distances in, 106

rate of growth in, 1 1 1

tools used in, 126

wages in, 125
Mandrel, 228
Mangabeira rubber, 28
Manitoba rubber, 26
Manihot dickototna, 26, 204
Manihot Glaziovii (Ceara rubber),
6, 8, 24, 43, 197, 200 et seq.

formation of latex vessels, 47

laticiferous system of, 202

wound response in, 59
Manihot heptaphylla, 26
Manihot piauhyensis, 26
Manufacture of latex, 69

of rubber goods, 220 et seq.

calendering, 227

colouring matter, 224

drying, 222

mastication and mixing, 223

sulphur in, 224

vacuum driers, 223

washing, 221

Manuring, 115, 116

at Peradeniya, 116

green, 117

phosphates, 116

potash, 116

Mariaella Dussumieri, 181
Markets, rubber, 169
Markham, Sir Clements, proposes

plantations, 5

Marking the tree, 140 et seq.
Mascarhenasia elastica, 34
Mauritius, 7
Medullary rays, 44, 49
Mexico, Guayule rubber, 30

rubber planting in, n
Million acres, produce of, 13
Morris, Sir Daniel, on Ficus elastica,

208
Motor tyres, 228, 232

Nerve, 171

New Guinea, 36

Nigeria, Southern, Funtuwia'm, 207

Nodules, 192

outbreak in Ceylon, 193
Nurseries, 99
Nyassaland, Ceara in, 204

Oil, from rubber seeds, 121
Omaquas Indians, 4
Overtapping, 78

Packing, 168

Pao di Xirringa (syringe tree), 4,

21
Para, hard, price of, 14

rubber, 3, 21, and see Hevea
brasiliensis

rubber, export of, 4
Parameria glandulifera, 35
Paring, basal system, 139

full herring-bone, 139

full spiral, 139

half-herring-bone, 137

half-spiral, 139

physiological effect of, 79

process, 143

systems of, 137
Parkes' cold process, 233

RUBBER PLANTING

243

Parkes, discovery by, 218
Parkin, experiments by, 60

incision method employed by,
64

pricking methods, 131
Parthenium argentatum (Guayule

rubber), 29
Pearson, H. C., 230
Peradeniya, Ceara at, 204
Petch, T., on blemishes in rubber,

I7,3 ,
on dead stumps, 195

on fames semitostus, 185

on tackiness, 175
Phloem tubes, 41, 45, 49
Phosphates, in manuring, 116
Physiology of latex production,

38

Phytophthora Faberi, 187
Pink disease (Corticium salmoni-
color], 190

Bordeaux mixture for, 190
Plantation industry, rise of, in the
East, 10

rubber, best form of, 170

yields, 151

yields, in Ceylon, 152

yields, in Malaya, 152
Planting distances, in Ceylon, 107

distances, in Malaya, 106

hexagonal, 108

on the square, 108
Polymerisation, 55, 215
Potash, in manuring, 116
Price of rubber, 14
Pricker, Bowman-Northway, 132
Pricking, by Parkin, 131

by Trimen, 131

effect of, 58

methods, 133

objections to, 132

Wright on, 130
Production from estates, 12
Pruning, 120

thumb nail, 120
Pure rubber, 210

composition of, 211

Quality, 171

Railway buffers, 228
Rainfall at Henaratgoda, 72

at Peradeniya, 61

effect on yield, 73
Reclaimed rubber, 234
Renewal of bark, 49
Resiliency of rubber, 171
Response of trees to certain stimuli,

65

Resting periods, 89
Rhizomorphs, 185
Roads, 103
Root rubbers, 33
Roots, diseases of, 183
Rubber, acreage under, 12

African species of, 30 et seq.

American species of, 17 et seq.

analyses of, 86

approximate composition of,
212

Asiatic species of, 34 et seq.

balls, early mention of, 3

biscuit, 154, 212

block, 164, 167

botanical sources of, 16

capital in, 15

chemical indifference of, 213

chemistry of, 210 et seq.

collection of, in Brazil, 19

defects in, 173

discovery of, 3

early uses of, i

estate, site of, 96

exports of, from Brazil, 4

exports of, from East, 13

globules, size of, 53

goods, manufacture of, 220 et
seq.

goods, testing of, 236

loss of weight in washing, 160

markets, 169

method of collection, 3

molecule of, 215 "

percentage in latex, 83, 92

physical properties, 212

planting, birth of industry, 5

price of, 14

quality of, 171

reclaimed, 233

244

RUBBER AND

Rubber, continued
resiliency of, 171
rings, 230
sales, 169
scrap, 1 68
seeds, oil from, 121
seeds, winning of, 6
sheet, 225
shoes, 230
smoking of, 165
soils, analyses of, 94
solution, 230
solvents, Weber on, 213
synthetic, 214 et seq.
vines planted in Congo, 209
washing of, 159

Sales, rubber, 169
Schidrowitz, 36

on intercrops, 114

on reclaimed rubber, 235
Science, applied to pests and

diseases, 177
Scott, Dr D. H., 47
"Scrap, Ceara," 25

rubber, 168

Seasonal variation in latex, 71
Seed bearers, 102

selection, 101

selection by progeny, 103
Seedling, laticiferous system in, 46, 47
Seedlings, in baskets, 100, no
Seringa, 4

Seringal or estate, 22
Seringueiro or collector, 4, 20
Shade belts, 119
Sheet rubber, preparation of, 225
Siam, 35
Singapore, 7, 8
Smoked sheet, 164
Smoking, 165

of wild rubber, 20
South India, labour in, 122
Spaniards, early employment of

rubber by, 3

Species of rubber, American, 17 et
seq.

African, 30 et seq.

Asiatic, 34 et seq.

Sphaerostilbe repens, 184, 187

Spiral system of tapping, 49

Spur-shaped pricker, 132

Stagbrook Rubber Co., crop of, 73

Stem, diseases of, 187

Stone cells, 44, 49

Stumping, 99

Sudan, 33

Sulphur, in rubber manufacture, 224

Sumatra, 35, 36

Synthetic rubber, 214 et seq.

discovery by Bouchardet, 215
Syringe tree, 4
Syringes, 4

Tackiness, 175
Tapping, age for, 128

average yields (grammes), 77

basal system, 139

difficulties, 149

effects of, 90

excision methods of, 136

experiments, 56

Fitting on, 48

herring-bone system, 133, 139

ideal rate of, 80

incision methods of, 130

increase of yield on, 61

intervals, 62, 75, 149

methods of, 57

moderate, 90

paring process, 143

precautions, 149

rules for, 92

severe, 90

spiral system of, 49

systems of paring, 137

time occupied in, 76

tools, 144

Tappings, results on intervals of, 62
Tea, as intercrop, 114
Teats, 230
Tephrosia, 113
Termes gestroi, 180
Thinning out, 121
Tilden obtains synthetic rubber, 214
Tisdall, W. N., estimate by, 127

on stumping, 109
Tobacco pouches, 228

RUBBER PLANTING

245

Tools, for tapping, 144

used in Ceylon, 126

used in Malaya, 126
Torquemada, Juan de, 3
Transport in Brazil, 23

in the East, 97

of latex, 156

Trimen, Dr, experiments in tapping
Hevea, 8

pricking by, 131

Ule rubber, 26

Ulequahuitl (Castilloa elasticd), 3

Vacuum driers, 163, 165

in manufacture of rubber, 223

"Vapourite," 181

Vegetative organs, 38

Vulcanisation, 2, 216 et seq.
cold, 218, 233
Goodyear's dry process, 231
hot, 217

in Amazon districts, 230
Hancock's wet process, 231
Parkes' cold process, 231, 233
time required for, 232
Weber on, 217

Vulcanite, 236

Wages, in Ceylon, 125

in Malaya, 125
Washing machines, 160
Water supply, effect on latex, 88
Weber, on rubber solvents, 213

on vulcanisation, 2, 217
Weeding, 1 1 1

West Africa, rubber planting in, 1 1
West Indies, 5, 7, 8
Wickham, H. A., 5

brings Hevea seeds to Kew, 6

smoking machine of, 166

Wild rubber, African, 30 et seq.

from Africa and Asia, 4

from Congo State, 5

replanting in Brazil, 209

smoking of, 20

tapping of, 20

trade in, 4
Willis, Dr J. C-, 56

* experiments by, 60
Willughbeia, 35, 36
Wind, affects Hevea, 179

belts, 119
Wound response, 59

experiments in Ceylon, 60

in Castilloa, 59

in Funtumia, 59

in Hevea, 59

in Manihot, 59

increased yield attributable to,

61
Wright, Herbert, estimate by, 12

on pricking, 130

Yield, at different levels, 80, 81,

148

duration of, 64
effect of rainfall on, 73
from Henaratgoda tree, 66, 67
from tapping at frequent in-
tervals, 78
general considerations affecting,

87

in relation to bark, 66
in relation to volume of bark,

66

in grammes, 77
per acre, of dry rubber, 64
per tapping, variation in, 72
plantation, 151
season of highest, 72
variation in, 74

CAMBRIDGE : PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS

Cambridge University Press

SELECTED LIST

Agriculture in the Tropics. An Elementary Treatise.

By J. C. WILLIS, M.A., Sc.D. With 25 plates. Demy 8vo.

75 6d net. Cambridge Biological Series.

' ' Alike in crop production and the breeding of live stock, the tropics
are being proved capable of achievements undreamt of a few generations
ago.... Mr Willis exhibits in his instructive volume an intimate knowledge
of the agricultural features of most of the tropical areas, and the information
he gives concerning the soils and climates, and the principal cultivations at
the present time, will be read with interest by those experienced in tropical
farming, and will be of inestimable benefit to intending emigrants and the
inexperienced. " — Field.

The Journal of Agricultural Science. Edited by R. H.
BIFFEN, M.A., A. D. HALL, M.A., F.R.S., andT. B. WOOD, M.A.
The subscription price, payable in advance, is 1 55 net per volume post
free. Separate parts 55 net each.

Mendel's Principles of Heredity. By W. BATESON,

M.A., F.R.S., V.M.H., Director of the John Innes Horticultural
Institution. Third impression with additions. With 3 portraits,
6 coloured plates and 38 figures. Royal 8vo. 125 net.

The Duab of Turkestan. A Physiographic sketch and
account of some travels. By W. RICKMER RICKMERS. With
207 illustrations. Large Royal 8vo. 305 net.

The Land of the Blue Poppy. Travels of a Naturalist
in Eastern Tibet. By F. KINGDON WARD, B.A., F.R.G.S. With
40 plates and 5 maps. Royal 8vo. 125 net.

Yun-Nan, the Link between India and the Yangtze.

By Major H. R. DAVIES, 52nd Oxfordshire Light Infantry. With
map and 73 plates. Royal 8vo. i6s net.

The Climate of the Continent of Africa. By ALEXANDER

KNOX, B.A. (Cantab.), F.R.G.S. With 13 maps and a diagram.
Royal 8vo. 2 is net.

An Atlas of Commercial Geography. Compiled by
FAWCETT ALLEN, Assistant Map- Curator to the Royal Geographical
Society. Containing an Introduction by D. A. JONES, Assistant
Librarian to the Royal Geographical Society, 48 maps, and an Index.
Demy 410. 35 6d net.

Cambridge University Press

Fetter Lane, London. C. F. Clay, Manager

Cambridge University Press

SELECTED LIST

Makers of British Botany. A Collection of Biographies

by living botanists, edited by F. W. OLIVER. With frontispiece and
26 illustrations. Demy 8vo. 95 net.

Herbals. Their Origin and Evolution. A Chapter in
the History of Botany, 1470 — 1760. By AGNES ARBER, D.Sc., F.L.S.
With frontispiece, 21 plates, and 113 illustrations in the text. Royal
8vo. i os 6d net.

The Genus Iris. By WILLIAM RICKATSON DYKES. With

47 coloured drawings by F. H. ROUND, i coloured plate of seeds by
Miss R. M. CARDEW, and 30 line drawings by C. W. JOHNSON.
Demy Folio. £6 6s net.

A Manual and Dictionary of the Flowering Plants

and Ferns. By J. C. WILLIS, M.A., Sc.D. Third edition.
Crown 8vo. los 6d. Cambridge Biological Series.

Trees : a Handbook of Forest Botany for the Woodlands
a,nd the Laboratory. By H. MARSHALL WARD, Sc.D., F.R.S.
Vol. I. Buds and Tivigs. Vol. II. Leaves. Vol. III. Flowers
and Inflorescences. Vol. IV. Frtdts. Vol. V. Form and Habit,
^v^th an appendix on Seedlings. With numerous illustrations. Crown
8vo. 45 6d net each. Price for the set of five volumes, 2os net.
Cambridge Biological Series.

Grasses : a Handbook for use in the Field and Laboratory.
By H. MARSHALL WARD, Sc.D., F.R.S. With 81 figures. Crown
8vo. 6s. Cambridge Biological Series.

Types of British Vegetation. By members of the Central

Committee for the Survey and Study of British Vegetation. Edited
by A. G. TANSLEY, M.A., F.L.S., University Lecturer on Botany in
the University of Cambridge. With 36 plates and 21 figures. Crown
8vo. 6s net.

The Elements of Botany. By Sir FRANCIS DARWIN, Sc.D.,

M.B., F.R.S., Fellow of Christ's College. Second edition. With
94 illustrations. Crown 8vo. 48 6d. Cambridge Biological Series.

Practical Physiology of Plants. By Sir FRANCIS DARWIN,
Sc.D., F.R.S. and E. HAMILTON ACTON, M.A. Third edition.
With 45 illustrations. Crown 8vo. 45 6d. Cambridge Biological Series.

Cambridge University Press

Fetter Lane, London. C. F. Clay, Manager / "^ ^

14 DAY USE

RETURN TO DESK FROM WHICH BORROWED

LOAN DEPT.

LD 2lA-60m-3,'65
(F2336slO)476B

General I
University of

Berkelc,