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Hawaii Agricultural Experiment Station,
TL S.IITH, SPECIAL AGENT IN C.
o ,, RESS BULLETIN No. 13 S H :
US. DEPOSITORY UBBER IN HAWAII. o'
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SA comparatively new industry, the cultivation of rubber-
producing plants, now engrosses the attention of planters in
all tropical lands. There are probably more new areas being
planted to rubber than to any other single crop, and much cap-
ital formerly invested in coffee, cinchona, tea, cotton and sugar
is being diverted to this new industry in the hope that the
profits will be greater than are now derived from older estab-
For those interested in new rubber plantations in Hawaii the
following notes in regard to the plants which are the chief
sources of the world's rubber supply may be of value. 1
In 1900 Africa produced 16,000 tons of rubber, America
31,466 tons, and Asia and Oceanica 2,339 tons, a total of ap-
proximately 50,000 tons. The world's production was esti-
mated at 53,887 tons in 1902, 55,603 tons in 1903 and 61,759
tons in 1904. The average price for "Fine Para" in Liverpool
has risen from 75 cents per lb. in 1902 to $1.14 in 1904, and has
not been less than $0.75 since 1895, and has not fallen below
$0.60 since 1877. This rise in price has been due to the greatly
increased demand for rubber in the arts and industries without
any corresponding increase in the source of supply. The out-
look is that the price of rubber will continue to rise until either
the price becomes prohibitive thus curtailing demand; or, an
artificial substitute for this valuable product is produced syn-
a thetically in the chemical laboratory; or, until the world's cul-
'This is mainly a compilation from the extremely valuable monograph
on the rubber plants of the world by Peter Reintgen: "Die Kautschuk-
pflanzen, Eine Wirthschaftsgeographische Studie," Tropenpflanzer, Vol.
VI, May, 1905.
tivated rubber plantations begin to yield to the full extent of
No extensive new rubber forests are likely to be discovered,
although investigators are almost daily adding names to the
l. Ifs lg't ts from which rubber may be secured. New rubbers
d..PI~e ~' 1l4e experimentation before their relative commercial
. value bee~2 s establishedd.
Artificia*s~ ers may resemble the natural article in some
rone of its chAtteristics but none have thus far been produced
'vhich fhehiquisite elasticity.
As to t e ,ijd solution, while there can be no doubt that
'. cultivated-fu%$bT plantations may ultimately supplant the prod-
e,^ e' Rwif trees, it will undoubtedly be a matter of decades
*. rt 'th ln years before even a parity between supply and de-
man .is reached. In the meantime the question arises, if we
are to plant rubber, to what particular variety shall we pin
our faith. A consideration of the climatic conditions under
which the various natural rubber producing plants thrive will
therefore first be necessary.
AMERICAN SPECIES OF RUBBER PLANTS.
In 1904 nearly fifty per cent. of the world's supply of rubber
came from the Amazon valley and the major share was classed
as "Para." Para rubber is, has been and probably will continue
to be the standard of excellence with which all other rubbers
are compared. It is in the main derived from a large tree,
Hevea braziliensis, Muell. Arg., which grows wild in the trop-
ical forest on the south bank of the Amazon and its tributaries,
the Rio Purus, Rio Jurua, Rio Negro, Rio Madeira, and Rio
Javary-Iquitos. So far as known, Hevea braziliensis only rare-
ly occurs on the north side of the Amazon, but its place is there
taken by other species of Heveas which yield rubber of inferior
quality and secondary value. Herea braziliensis is a stately
tree often reaching the height of 130 feet with a trunk 3 to I
feet in diameter, the crown not very large but somewhat dense.
The leaf is compound with three oval, sharp-pointed leaflets,
dark-green above, bright-green on the under surface and rather
prominently nerved. The flowers are small, yellowish-green,
and the fruit a 3-celled capsule with 3 seeds as large as hazel-
The trees are sparsely scattered through the tropical jungle
over a region as large as Europe, and it is said that the native
rubber collectors consider that a remarkably rich rubber dis-
trict where the rubber trees average one to the acre. The mean
annual temperature of the regions is about 83 F., with an
annual range between 730 and 950. The rainy season begins
in October. By January the whole region for 2,000 miles is
more or less submerged and the floods do not begin to disappear
until June. During the "dry" months, July, August and Sep-
tember, there are frequent thunderstorms. The home of this
tree is a hot, steamy, truly tropical, rich alluvial plain, almost
under the equator and only slightly elevated above sea level.
The tree seldom occurs at elevations greater than 600 feet. Its
native habitat, so widely different from the climate of Hawaii,
undoubtedly precludes the probability of its successful cultiva-
tion in these islands. There are eight or ten other rubber-yield-
ing species of Herea, some of them undescribed by botanists, all
native of the upper Amazon valley. While some of these grow
at higher elevations and in lands not periodically submerged
their total yield is comparatively inconsiderable in quality and
While Rubber. This is produced by a number of species of
trees of the genus Sapiunm, native in the north-western portion
of the South American continent.
Sapiunm Tolimense, Hort., is a native of the mountains in
South Western Colombia, making its best growth at an altitude
of 3700 to 6000 feet The tree is said to grow with extraordi-
nary rapidity, reaching a height of fifty feet with a trunk one
foot in diameter in six years. It will grow at a higher elevation
than coffee. The rubber is of very excellent quality. This is
certainly a promising variety for introduction into Hawaii.
Sapium. rerune Hemsl. A forest tree 60 to 75 feet high with
a trunk 3 feet. in diameter, native to Ecuador and southerfi
Colombia. It reaches its best development at an elevation of
5,500 to 7,500 feet and grows up to 10,000 feet. This tree is
the principal source of the "caucho blanco" of Ecuador.
Sapium stylare Muell. Arg. A large forest tree occurring at
an elevation of from 3,000 to 6,000 feet on the wet mountain
slopes from Venezuela to eastern Ecuador. The mean tem-
perature of the region where it grows ranges from 56 to 61 F.
Other species of Sapium growing under truly tropical condi-
tions at lower elevations are S. tapuri Ule., S. eylandulosum
Ele, S. utile Preuss, and S. Marmieri Huber. The milky sap
of the latter is poisonous. These species all require higher
temperatures and a greater degree of humidity than is found
Black Rubber, or Central American. Rubber.
The chief source of this rubber is Castilloa elastica Cerv. It
is a native of the western slope of the Andes of Peru and Ecua-
dor up through Central America to Mexico. The tree grows
to the height of 40 to 60 feet in the open, but often reaches
120 to 150 feet in height and 6 feet in diameter in the dense
and hot tropical forests. Unlike Hevea it will not stand wet
feet but requires good drainage. It is never found in wet or
swampy localities and grows best at the lower elevations in hot,
sheltered inland valleys. In the equatorial belt Castilloa oc-
curs up to 2,500 fee t but at 15 either side of the equator does
not grow well above 1,600 feet. It requires rich alluvial well-
drained soils, high temperatures and shelter from winds.
The optimum mean annual temperatures for the growth of this
tree range from 770 to 82' F. It grows in Mexico where the
mean yearly temperature is 720 F. and will stand a much
lower one, but as the temperature and humidity decrease the
growth of the tree is slower and the yield of rubber rapidly
The leaves of Castilloa elastica are heart-shaped at the base,
entire, bright-green and shining, those of young trees 20 inches
long by 7 inches wide, those of old trees 6 to 12 inches long
by 2 1-2 to 5 inches wide. The trunk of the tree is wing but-
tressed at the base. Rubber collectors distinguish 3 varieties
depending on the color of the bark and twigs, but botanically
all are considered one species.
Castilloa. elastica. has been widely planted. Five hundred
thousand trees of this variety have been planted in the vicinity
of Bluefields, Nicaragua, during the last seven years. The first
of the planted Castilloa forests in Nicaragua has been tapped
this year. Six thousand seven-year-old trees yielded 534 pounds
of rubber, an average of 1 1-3 ounces per tree. A few of the
largest were tapped repeatedly at 2-week intervals without in-
jury and yielded an average equal to that secured at the first
tapping. In the regions climatically suited to it Castilloa is
considered one of the surest and most reliable species in the
cultivation of which it is safe to invest the large capital re-
quired to plant and care for an artificial forest up to the time
when dividends may be expected. However, it is doubtful
whether its cultivation should be attempted on more than an
experimental scale in Hawaii. Our mean annual temperatures
and mean humidity are too low, and also the islands lie within
the zone of the trade-winds, and lack the tropical climate of
other island groups in equal latitudes.
Ceara Rubber is derived from a small tree usually (in Ha-
waii) not exceeding 25 to 30 feet in height, IManihot Glaziowii
Auell. Arg. This tree is a native of southern Brazil. It grows
on hot desert-like sandy plains and along the granitic ridges
in a region devoid of running streams and with only a sparse
cover of desert shrubs and low trees. The mean annual temper
ature of this region ranges from S23 to 90 F. The rainy sea-
son resembles that of Hawaii in that there are only occasional
rains during the wet months from November to May, or June,
but differs from Hawaii in that the rainy season comes in sum-
mer. Although the tree is at its best in this hot desert country
it extends inland to the foot-hills, where the rainfall averages
about 100 inches and where the night temperatures often fall
to 60: F. or less. Like Castilloa elastica, the Ceara tree re-
quires good drainage and never thrives in wet or swampy soils.
Ceara rubber trees will grow in a very wide range of situa-
tions. It makes an extremely rapid growth in Hawaii, thriv-
ing from sea level up to 2,500 feet on both the dry and wet
sides of all the islands.
The tree is being largely planted in all tropical and sub-
The seeds are about the size of small plum pits and mottled
like castor bean seeds. When planted they take a long time to
germinate, unless the hard, stony outer coating is filed or
abraded. Plant the seed where the tree is to grow either at
irregular intervals, if in gulches or along stony ridges or
other waste land, or if tillable land is to be used plow
and prepare the whole field, or plant in a hole, as is often prac-
tised in the case of bananas. The distance apart should be
from 6 x 10 to 12 x 15 feet, which would give from 24-0 to
726 trees per acre. If tillable land is used it will pay to culti-
vate and fertilize. On gulch, mountainous and waste lands
the weeds and grass must be cut out and a space hoed around
the foot of each tree as often as necessary.
A number of Ceara rubber trees were planted in 1893 on the
land now occupied by this Station. A tree standing alone near
the Tantalus road in the upper forest in the midst of a clear-
ing, and which has been somewhat spasmodically cared for is
about 40 feet high with a trunk 10 inches in diameter. Other
trees planted along the trails and absolutely neglected for 12
years, overgrown by lantana and over-shadowed by Eucalyptus
are now little more than 12 to 15 feet high with a trunk the
size of a man's finger. So it pays to take care of trees even
though common report has it that "no cultivation is required."
This formerly unimportant but of late years much-talked-of
rubber is derived from Hancornia speciosa Muell. Arg. It is a
medium-sized tree native to the dryer coastal plains and up-
lands from Venezuela to southern Brazil and from the Atlantic
to the eastern foothills of the Andes in Ecuador, Peru and
Bolivia. Unlike the Ceara, this tree bears rubber in every part
of the plant, in the bark, wood, leaves and grben fruits. The
milky sap which flows from wounds becomes rubber without
other treatment than exposure to the air. The flow of milk sap
is greatest during the summer months. Although Hancornia
speciosa is of very slow growth it is being substituted for cof-
fee by many planters in southern Brazil who see only small
profits in that business for many years to come.
The tree grows on a great variety of soils, and is easily propa-
gated from cuttings. The leaves are about 2 inches long by 3-4
to 1 inch wide, acute at the base and blunt at the apex. The
fragrant white flowers are about 1 inch across. The fruit is
a greenish-yellow berry streaked with red, and is edible. The
rubber is white and of very good quality.
These species of rubber plants are the chief sources of the
American rubber supply. The genera Herea, Manihot a.nd Sa-
pium belong to the Euphlobiaceae or Spurge family, well known
members of which are the Castor Bean, Tua-Tua and Cassava.
The milky sap which yields the rubber is contained in milk
tubes in the inner or growing portion of the bark. Hancornia
belongs to the botanical family Apocynaceae, while Castilloa is
one of the Moraceae, a family including the fig and bread-fruit.
Of the 31,462 tons of rubber exported from South and Cen-
tral American ports in 1900, 25,500 tons were derived from
trees of the genus Hevea, 4,700 tons from Castilloa and Sa-
pium (40% Sapium and 60o% Castilloa) and 1,250 tons Ceara
and Pernambuco rubbers.
AFRICAN RUBBER PLANTS.
The African rubber supply is very largely derived from spe-
cies of vines of several genera belonging to the botanical order
Landolphia Hendelottii D. C. is a woody, slow-growing vine
native to the dry hot open country from Senegambia to the
western Soudan, between 90 and 12' N. latitude. While this
is an important source of rubber it is considered unsuited to
cultivation because of its very slow growth. It takes twenty
years to attain full maturity.
Landolphia owcarienlsis Beauv., grows in the great tropical
forest region of western Africa. About half of the Kongo rub-
ber comes from this vine. A characteristic of this species as yet
unexplained is that individual plants growing side by side, and
apparently identical, show wide variations in the amount of
rubber which they yield,-a fact tending to discourage cultural
experiments with this species.
Landolphiia Klainei Pierre. Native of the Kongo forests, is
considered worthy of cultivation in tropical forest regions be-
cause of its great rapidity of growth. It produces a rose-col-
ored rubber of high value.
Laqndolphia Kirkii Dyer, is the most important rubber-yield-
ing vine of east Africa. extending from the Portuguese posses-
sions to Victoria Nyanza. It is the source of "Mozambique"
rubber, which is worth about 3-4 as much as "Para."
There are many other species of Landolphias but these are
economically the most important.
There are also a number of species of Clitandra and Carpo-
dinus of greater or less value as rubber-producing plants.
Root rubber is derived from the roots of various herbaceous
plants that grow in the open prairies or savannahs in central
west Africa. The plants are pulled up by the roots, these cut
off, dried in the sun and the bark peeled. The dried bark
is pounded in stone mortars until the woody portion
is pulverized. The rubber is gathered together, pressed into
balls or cakes and is ready for export. About 1,500 tons of
root rubber is the average annual crop. It is worth about 60%
as much as Para. It is derived from the following species of
Landolphia Thollonii, Dewevre. A woody perennial 6 to 12
inches high with strong horizontal creeping root stocks extend-
ing many yards under the surface of the ground. It grows in
very dry, sandy soils in regions subject to annual prairie fires,
so that while it is undoubtedly an attractive plant for cultural
experiments, seeds are not easily obtained. The underground
rhizomes are very rich in rubber.
Carpodinus chYtqlorrhi za K. Schum.. and C. gracilis Stapf,
yield a very elastic brownish-red rubber. They are low shrubs
2 to 5 feet high, native of dry, desert regions of central west
Africa, little known botanically, but quite important as sources
This is derived from the milky sap of an Apocynaceous tree
Kickxia elastica Preuss, native of the tropical regions of west
Africa from Kameroon to the Gold Coast. It is considered one
of the very best of the recently discovered rubber-pro.ducing
species. In its home it grows from a few hundred to 3,000 feet
above sea level and is said to require about the same climatic
conditions as cacao. The milky sap of this tall forest tree is
extraordinarily rich in rubber of a superior quality, as high as
58% having been found. A seven-year-old tree is reported by
R. Schechter as having yielded 70.5 ounces of rubber which
dried to about 60 ounces.
The sap is collected, mixed with 3 to 6 times its volume of
water and is then boiled. The rubber rises to the surface, is
skimmed off, washed in cold water and then pressed into sau-
sage-shaped masses. Various salts and acids are also used for
coagulating the sap without heating it. The tree is a large one,
often reaching 100 feet or more in height, and in favorable
situations growing with extraordinary rapidity. It does not
seem to be especially particular in regard to its soil require-
ments, but undoubtedly requires high temperatures and a high
degree of humidity.
ASIATIC RUBBER PLANTS.
The Asiatic rubbers are derived from both trees and vines.
Assam rubber. This comes from the well-known "Rubber
Plant" of the horticulturist, Ficus clastica Roxb. This enor-
mous forest tree is a native of the valleys and lower slopes of
the whole southern Himalayas, also extending through the
countries of southern Asia to Java and the Malayan archipelago.
It often grows to a height of 150 to 180 feet, with a clump of
trunk-like aerial roots many yards in diameter. The seeds of this
tree usually germinate in the top of some nearby tree of a dif-
ferent species, and throw out long aerial roots which at first
hang pendant but on reaching the ground themselves throw out
feeding roots and increase in diameter until they reach trunk-
like proportions. One of these air-roots if destroyed at the
base will die below the point of injury but will throw out new
aerial roots above, these in turn lengthening until they reach
the ground and again throw out feeding roots. In
this regard Ficus elastica is similar to the Ohia Lehua of the
windward forests of Hawaii with its much-branched and many
bodied trunks which in the beginning were really the aerial
roots of the epiphytic ohia seedling.
In its native habitat this tree grows best at an elevation of
from 2,000 to 3,000 feet at from 25 to 27 north latitude, and,
nearer the equator, reaching to fully 5,000 feet. The tempera-
ture ranges from a winter minimum of 48 to a summer max-
imum of 92 F., with a yearly mean temperature of 73 -. The
rainfall of the forest zone where this tree grows ranges from
75 to 100 inches or more. The soils are somewhat rocky, either
volcanic or sedimentary. The yield of rubber varies widely.
In the total yield from individual trees this species excels all
others. P. van Romburgh secured the enormous yield of 405
pounds of rubber from a very old tree in western Java (near
Buitenzorg). A 23-year-old tree on an equatorial plantation in
Borneo yielded 32 pounds of rubber at its first tapping. In As-
sam trees averaging 100 feet in height, which had not been
tapped for 15 years previously, yielded an average of 10 lbs.
of rubber, the next year 4 lbs. and the third year only 1.8 lbs.
In New Guinea 8-year-old trees of Ficus elastica yielded 5.7
lbs. of rubber within a week. The growth of this tree is some-
what slow in Hawaii; nevertheless I believe that it is one of the
most promising rubber trees for plantation culture, especially
in such districts as Hilo, Puna, Olaa and Nahiku, where the
rainfall is high. Ficus elastica will stand low temperatures
that are extremely detrimental to the Para and Central Ameri-
can rubber trees.
Practically all the rest of the Asiatic rubbers are derived
from vines. It is doubtful whether any of these could be suc-
cessfully and profitably transplanted to Hawaii.
THE BEST RUBBER TREES FOR HAWAII.
Hawaii with its subtropical rather than truly tropical cli-
mate, is limited to a very few species of rubber-producing
plants. The most suitable species of those above enumerated
are undoubtedly in the order of their importance Manihot Gla-
ziolii and Ficus elastica. The first of these, the Ceara rubber
tree, should comprise the larger proportion of all new planta-
tions, because of its extremely rapid growth and early maturity.
In laying out a rubber plantation comparatively early returns
are desirable. The Ceara trees will stand a moderate tapping
when three years old, and may be counted on to yield a-consid-
erable return in five years.
The Assam rubber tree, Ficus elastica, while of much slower
growth, yields much more abundantly when it does finally reach
a bearing age. This is also true of the Manicoba rubber, Han-
cornia speciosa. The white rubbers, Sapium Tolimense, S. ve-
rum and S. stylare, native of high elevations where the climatic
conditions are similar to those of our own mountain slopes,
would seem to be promising for experiment, provided seeds can
WILD AND CULTIVATED RUBBERS.
Practically all the rubber thus far marketed has been derived
from wild trees. The collection of rubber by the native races
of all countries has been extremely destructive, in many in-
stances resulting in the extermination of the rubber-producing
species over wide areas. This factor alone has had much to do
with the rapid rise in value of this article. The discovery of a
new rubber-bearing species or of a new forest in some hitherto
unexplored region means the rapid destruction of this source
of supply, because governmental control of the native rubber
gatherers is absolutely impossible, and attempts at restraint or
supervision worse than futile. The native collector wants to
get as much as he can today, so that he will not have to work
tomorrow. Enormous forest trees, perhaps hundreds of years
old, are felled or hacked and mutilated so that they soon die and
rot, and for his trouble the native secures on an average hardly
one per cent. of the total amount of rubber in the bark, but that
which he gets costs him only the labor of gathering it. There
is no investment of capital. No taxes have been paid on the
lands producing the raw material, and there has been no ex-
penditure for labor or permanent improvements and executive
management of the enterprise.
In the case of a plantation for the production of rubber on a
commercial scale, the points to be considered are not merely
the adaptability of certain rubber-bearing species of plants to
certain soils and climatic conditions, but it is fully as impor-
tant to so conduct the enterprise during the first unproductive
years that the total capital invested when production finally be-
gins shall not be so large as to preclude the possibility of aver-
age dividends. The robbery of cultivated trees after the man-
ner of the native rubber collectors is of course entirely out of
the question. A plantation management must evolve methods
of gathering rubber in such a manner that the trees will not be
destroyed and yet so that they will produce to the very maxi-
mum of their capacity. Fungus diseases and insect pests will
undoubtedly appear. The question of how much or how little
cultivation is necessary will have to be worked out in a prac-
tical way. In other words, the cultivation of rubber is an ex-
periment and until it has passed the experimental stage no one
knows to what extent it will be profitable.
'The outlook is good viewed from the standpoint of an in-
creasing demand for the product.
Conditions in Hawaii are apparently extremely favorable for
the cultivation of the Ceara trees. One of the newly formed
companies have already planted 100,000 seeds of this species.
and expect to have half a million trees growing within another
two years. If our planters succeed with rubber as they have
with sugar, and put into the business as much science, skill and
knowledge as they would into any other new enterprise there
can be absolutely no question of ultimate success. The planters
of Hawaii stand on an equal footing with those of any other of
the tropical countries of the world in that the cultivation of
rubber is as yet everywhere only an experiment.
JARED G. SMITH,
Special Agent in Charge of Hawaii Experiment Station.
HONOLULU, H. T., July 20, 1905.
PARADISE OF THE PACIFIC PRINT
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