Physiological Principles

for Determining the
Value of the various

RUBBER TAPPING
METHODS.

^*r

SI

BY

PROFESSOR DR. HANS FITTING,

STRASSBURG i. E.

$

<§>©

SI

WITH FOUR DIAGRAMS.

[Translated by J. H. BENTON.]

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"Times of Ceylon " Office, 27, Mincing Lane,
LONDON, E.C.,

and " Times " Buddings, Colombo, CEYLON.

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Physiological Principles

for Determining the
Value of the various

Rubber Tapping Methods,

Founded on some Experiments made on Hevea Brasiliensis.

BY
PROFESSOR DR. HANS FITTING,

STRASSBURG, i. E.

WITH FOUR DIAGRAMS.

Translated from the Gcniuin b\ J. H. Renton, and

Published bv kind permission of the Editors of the

" Tfopenpflanzer," Heilin.

Price Is. & B 1.

CAPPER cS: SONS:

Times of Ceylon Office, 27, MiXClXG L,\\K, LONDON, K.C. ;
AXD "TlMKS" Hl'ILDIXCiS, COLOMBO, CEYLON.

13

CONTENTS.

INTRODUCTION

PART I. — Physiological Starting Points for the Investi-
gation

A. Influence of Incisions in the Bark on the

Life of the Tree

B. Applicability of the Facts enumerated to

Rubber Trees .

C. Influence of Incisions on the production of

Latex in the Bark .

D. Problems for my Experiments

PART II.— My Experiments

A. Influence of Girdling on the distribution and

circulation of Sap in the Stem of Hevea

B. Influence of the Tapping Incisions on the

distribution and circulation of Sap in the
Stem of Hevea .

PART III. — Inferences and fresh Problems resulting
from my Experiments

PART IV. — Comparisons between my Observations and
the Experiences of practical Planters

PART V. — Value of the various Tapping Methods in
vogue judged from the points of view
attained .

PART VI. — Suggestions for Rational Tapping Methods

TRANSLATOR'S PREFACE.

The great importance which the Rubber Planting Industry
in the East has attained during the past few years must be my
excuse for offering to my fellow planters an English translation of
Professor Fitting's treatise on Rubber Tapping Methods, which
appeared as a supplement in this year's February number of the
" Tropenpflanzer."

Professor Fitting is one of Germany's first physiological
botanists and I feel sure that his views will be of interest to and
carry weight with those engaged in producing rubber in Ceylon
and Malaya.

I hope that his advice will be followed, and that serious
endeavours will be made to find out by further research and
experiments on a larger scale the very best method for harvesting
rubber.

I think I have succeeded in giving the exact sense of
Professor Fitting's very instructive treatise, but it is not possible
to translate a German scientific work literally without rendering
the translation heavy and un-English, though I have endeavoured
to adhere as closely as possible to the German text.

I wish to take this opportunity of expressing my very
sincere thanks to Professor Fitting and to the Editors of the
"Tropenpflanzer" for allowing the publication of an English
version. Mr. F. Crosbie Roles, of Ceylon, has kindly helped me
to see this pamphlet through the press.

J. H. RENTON.
Christmas, 1909.

PREFACE.

\Yhen I went to Java in the Autumn of 1907, having obtained
the German so-called Buitenzorg grant, it was, amongst other
things, mv intention, bv studying: rubber plants in the tropics, to

ERRATA.

Page n, line 5 — read organic instead of inorganic.
Page 14, footnote — read Fo/. 94 instead of Fo/. /. gj.
Page 22, footnote — read Icintlosc instead of cevnlose.
Page 45, line 20 — read bark instead of latc.v.

Page 48, line 16 — read distribution of substances instead of sap
distribution.

are imperative in order, by introducing rational tapping methods,
to protect rubber plantations against very unpleasant earlier or
later injuries. It is extraordinary, that the opinions on the advan-
tages of the various tapping methods so far recommended, are
not based on experiments, such as our general physio-
botanical knowledge suggests, and which have a definite
object in view. It is likewise strange, that there is an utter lack of
effort, by minute scientific research, to clear up the points
on which the experiences of planters are at variance.
Consequently a great uncertainty of opinion still prevails, which
can only prejudice the cultivation of rubber. I\. < o^m/nl
authorities in the field of rubber investigation have not bri-n able
to shut their eyes to this fact. From the literature on the subject

TRANSLATOR'S PREFACE.

The great importance which the Rubber Planting Industry
in the East has attained during the past few years must be my
excuse for offering to my fellow planters an English translation of

Tanninf A'fpfhnds. which

A 1VJ1V-OOVJJL A ILLlilg O V l_ 1 y 1 11O LI U>_ LI V >_ LI l_,O. LI 3 L, UHL 1L 13 11OL

to translate a German scientific work literally without rendering
the translation heavy and un-English, though I have endeavoured
to adhere as closely as possible to the German text.

I wish to take this opportunity of expressing my very
sincere thanks to Professor Fitting and to the Editors of the
" Tropenpflanzer " for allowing the publication of an English
version. Mr. F. Crosbie Roles, of Ceylon, has kindly helped me
to see this pamphlet through the press.

]. H. RENTON.
Christmas, 1909.

PREFACE.

When I went to Java in the Autumn of 1907, having obtained
the German so-called Buitenzorg grant, it was, amongst other
things, my intention, by studying rubber plants in the tropics, to
help to extend our knowledge of the utility and advantages of the
various tapping methods that had been described already. This
object can be obtained by research in two directions : firstly, on
anatomical lines, by studying the process of development
of the laticiferous system, the expansion of this system during
the diameter growth of the trees, and the renewal of the latex
ducts after the infliction of large wounds on the bark, such as
those made for the purpose of obtaining rubber ; and secondly,
on physiological lines, by ascertaining and investigating
all the various influences which tapping has on the vitality of the
tree and its component parts, as well as on the renewal of its
latex and rubber. Every physiological botanist, who has taken
the trouble to wade through the existing voluminous literature
on the subject of rubber cultivation, must arrive at the conclusion
that all these investigations, especially the physiological ones,
are imperative in order, by introducing rational tapping methods,
to protect rubber plantations against very unpleasant earlier or
later injuries. It is extraordinary, that the opinions on the advan-
tages of the various tapping methods so far recommended, are
not based on experiments, such as our general physio-
botanical knowledge suggests, and which have a definite
object in view. It is likewise strange, that there is an utter lack of
effort, by minute scientific research, to clear up the points
on which the experiences of planters are at variance.
Consequently a great uncertainty of opinion still prevails, which
can only prejudice the cultivation of rubber. Kecognixrd
authorities in the field of rubber investigation have not been able
to shut their eyes to this fact. From the literature on the subject

it would almost appear, as if in this connection it was not yet
sufficiently recognized, how important it is that theoretical and
practical research should go hand in hand. If from the very first
an endeavour had been made to keep in close touch with scientific
botany, I feel sure that many mistakes in the cultivation of rubber
would have been avoided, mistakes, the consequences of which
may for many years injuriously affect many plantations. Rubber,,
more than any other cultivation, stands in need of being constantly
supported by science, because in rubber planting many very
complicated scientific problems of various sorts have to be
considered, which cannot in any way be solved without due regard
to theoretical botany, and in practise very important demands are
made, the fulfilment of which must greatly depend on the solution
of these problems. For the more the world's production of
rubber increases, and the price drops, the more necessary it is
for producers, by rational methods, to get the most out of their
plantations.

As a whole series of questions for investigation actually force
themselves on any physiological botanist, who wishes to decide
on the suitability of the various tapping methods that have been
recommended, it seemed to me a profitable task, to determine,
whether research carried out from scientific points of view might
not promote our knowledge of the practicability of the tapping
systems considerably, and should this supposition prove correct,
to show the way we should follow in investigating the tapping
methods with regard to their utility.

Before beginning my investigations, I inspected a number of
old rubber plantations, noted for their excellence and productive-
ness, and in conversation with planters, obtained a certain amount
of insight into their methods, experiences and results. A stay in
Ceylon offered the best opportunity for this.

Hevea offered itself, so to speak, of its own accord as a fitting
object for my experiments. Firstly, it still occupies the first
place amongst rubber plants. With regard to no other tree,
therefore, is it of such pressing importance to increase our
knowledge of the utility of the various tapping systems. Secondly,
Hevea was the only rubber plant, of which at Buitenzorg in Java,
I was able to obtain some specimens for my experiments. I should
not like to miss this opportunity of expressing my warmest thanks
to the highly esteemed Director of Agriculture, Professor Dr.

Treub. for the kind way in which he met my requests. In the
same way I owe grateful thanks to the Directors of the Large and
Small Botanic Gardens, Mr. Pit and Dr. Tromp de Haas.
Both these gentlemen were constantly ready to assist me. Mr. Pit
had also the great kindness to let several older Hevea trees be
tapped according to my directions for some months, and to
sacrifice them afterwards for an examination. Dr. Tromp de Haas
with equal kindness, caused the incisions in some plants to be
covered with soil and coconut fibre. It is conceivable that the
number of old Hevea trees that could be placed at my disposal
in Buitenzorg was not sufficiently large to enable me to solve the
tapping problem completely. Too much must, therefore, not be
expected from my experiments. They can do no more than point
out a way, which by experiments on a larger number of trees,
might lead us in a comparatively short time to a comclusion as to
which of the tapping systems must be condemned as harmful.

But anyhow, my experiments will supply many valuable data,
on which it will be possible to base decisions with regard to the
various tapping methods, at least as far as Hevea is concerned.
How far the conclusions at which we have arrived in the case of
Hevea are also applicable to other rubber plants, future
experiments alone can decide.

PART I.

PHYSIOLOGICAL STARTING POINTS FOR THE

INVESTIGATION.

If a physiological botanist wants to form a right decision
on the suitability of this or that tapping method, he will above all
find it necessary to decide — and this at first apart from all practical
questions — in what way the tapping cuts affect the vitality of the
tree, and therefore, also the renewal of latex, and whether they
will not sooner or later hinder the further development of the tree.
For if they injure the tree, its growth must after a certain time
be retarded, and the latex, on account of insufficient renewal,
must gradually deteriorate and become poorer in caoutchouc.

A. Influence of Incisions in the Bark on the Life of the Tree.

I think we can take it for granted that every tapping system will
have at least some injurious effect on the tree. For every tapping
incision wounds in no small degree a living part of the tree, namely
the bark. But how can such an interference injure the tree ? In
order to answer this question, which is a very complicated one,
•certainly more complicated than may be imagined in planting
•circles, it will first of all be necessary to refer to the grn.T.il
nutritive relations, which must exist between the various parts of
the tree, in order to insure its normal existence and growth. \\V
are lucky in being able to make well-founded statements about
these relations, and to ignore everything hypothetical, and can
thus base our decisions on a sure foundation.

Two parts of the tree co-operate in providing it with the
nourishment that is absolutely necessary to make it live and grow :
the root system and the crown of the tree.

The root-system supplies simultaneously thr imli>prnsal>lo

10 —

water as well as the inorganic nutrient salts of the soil, which are
chiefly required for the formation in the plant of the organic
combinations containing nitrogen, sulphur and phosphorus. In
order, however, , to fulfil their chief function, the absorption of water
and salts in a profitable and sufficient manner, it is necessary for the
root-system to be well developed and healthy. It is likewise
necessary that the development of the root-system should keep
pa'ce with the growth of the other parts of the tree, so that it can
satisfy the constantly increasing demands for the supply of water
and nutrient salts made on the roots by the continuous develop-
ment of the crown.

The crown, on the other hand, provides the tree, that is.
the whole tree in all its parts, and thus also the roots, with the
organic products formed from the organic substances employed
in the construction and nutrition of the tree, in that the leaves, with
the aid of sun-light, extract carbon from the carbon dioxide of the
air an-d convert it into sugar. It is immaterial to us, in what part
of the plant the organic combinations containing nitrogen, sulphur
and phosphorus, necessary for the construction of all the organs of
the tree, are formed from this product of assimilation and the nutri-
ent salt? of the soil. We will therefore only mention the fact that a
great number of these substances appear to be produced in the
leaves, and this during the presence of sunshine. However that
may be, it is necessary under all circumstances, that the water and
salts from the soil should be transported upwards from the roots,
into the other parts of the tree, especially into that part above
the soil, which grows most extensively and vigorously, namely
the crown ; and that, on the other hand, the products of assimilation,,
sugar and other complicated organic substances from the crown,,
be conveyed to the other parts of the tree, and down to the
vigorously growing roots.

The sole connecting link between the root-system and the
leafy head is the stem. It must therefore contain the means of
transport for the organic and inorganic substances. The transport
of substances in the stem can take place in sufficient volume only
if the channels ,work normally and suffer no interruption. It
would, however, be a mistake to assume that the inorganic salts
and the water of the soil are transported in the same channels as
the organic substances. We are aware that four different principal
parts can be distinguished in the stem: the pith, the wood, the

— II —

bast and the cortex, with its suberous tissue, or bark. Careful
physiological investigations have shown that the ascending move-
ment of the salts and water of the soil takes place chiefly in the
wood, while on the other hand, the descending movement of the
iflorganic substances towards the roots takes place chiefly in the
bast, and possibly also in the cortex. Only in the case of a very
few plants does the pith participate largely in this transport, namely
in the case of those trees, where the pith contains a so-called
inner bast.

It has been my experience that in all tissues suitable for
sap-transport, the descent takes place chiefly, and quickest,
in a straight direction parallel to the axis of the tree.
It appears that those rows of cells take the chief part in the
transport which run in an upward verticle direction in the stem,,
and the cells of which inter-communicate. If the organic
substances are forced to descend in an oblique instead of a
straight direction, the progress of sap circulation will become
markedly slower.

But the parts of the stem not only perform the function of
channels for the constructive substances, they also form excellent
reservoirs for the temporary storage of those organic constructive
substances, which cannot be utilized at once, and which have beea
produced in excess. It is also of great importance to know, that
not only the channels which most rapidly transport the organic
substances, namely the bast and the cortex, form such reservoirs,
but so do all other parts of the stem, including the pith and the
wood, with its medullary rays, as long as they contain living cells.
The large; quantity of carbohydrates, particularly starch, which in
many trees is found in the living cells of the pith and wood are
nothing else but stored reserve material. As soon as they are
required, they can be conveyed from the reservoirs and used for
the growth of the stem or of other -parts of the tree. The
reservoirs, at least those contained in the wood, are filled from
the leaves by means of the normal channels which exist in the
trcv for the transport of organic substances: namely the bast and
the cortex. The most important subsidiary channels arc the
medullary rays, which penetrate deep into the wood. They also
transport the reserve material from the wood back again into
the chief channels.

It is easy to see how highly advantageous it is for the \iulity

12

of a tree, that the stem is not only a channel for nutrient
material, but also a reservoir for reserve material. If by some
influence or other the channels for the organic substances become
interrupted, it will through this arrangement be possible for the
roots and the stem to continue their growth for a long time in
quite a normal manner, by bringing the reserve material into
action. They will possibly be able to do this sufficiently long until
by reason of the tree's activity, the continuity of the channels has
been restored and the damage repaired.

A very simple experiment will give us a clear idea of
the functions of the various parts of the stem as channels for the
•organic and inorganic nutritive substances, and as reservoirs for
the reserve material. It is the well-known experiment of
girdling the tree. If we interrupt somewhere on the tree the
•continuity of the cortex and bast, by cutting two circular incisions
round the ,stem, some centimetres or so apart, and if we remove the
strip of cortex and bast between the two incisions down to the
wood, the leaves do not wither (provided that the wood thus
exposed is protected against desiccation), the crown continues to
grow undisturbed, and produces new organic matter, and there is a
•continuous increase in the ash-constituents of the crown ; all this
proves that the channels in the wood for the transport of water and
salts have not been interrupted by this interference. Also the
downward transport of the assimilated organic substances from
the leaves continues as before. But these organic substances can
no longer be conveyed in sufficient quantity as far as the roots, as
on account of the girdling the corresponding channels have lost
their connection; an accumulation takes place above the ring and
there all available reservoirs in the wood, pith, bast and cortex
will be crowded with reserve material. As the after-flow of
nutritive matter from the leaves into the parts of the tree below the
girdle has entirely stopped, the tree will in time be obliged to draw
here on all its reserve material in order to supply the matter
required for the further growth and sustenance of this part of the
stem and for the root-system. While thus in all parts of the stem
above the girdle more and more reserve material (for instance
starch) is being accumulated, it is on the other hand, noticeable
that below the girdle starch gradually disappears from all parts
of the stem. Evidently the wood can no longer obtain any
appreciable fresh supply of organic substances.

What will be the fate of such a girdled tree ? That must
depend entirely on whether the connection between the portions,
of bark will after some time be re-established or not. Soon after
the operation of girdling, a process of growth of a peculiar kind
that tends to close up the wound, is noticeable on the girdle. On
the two incisions, chiefly through the activity of the cambium,,
protruding pads of cortex arc formed, that are termed wound-calli.
These pads grow upwards and downwards towards each other
across the exposed wood, till they touch and at last coalesce.
When coalescence has been accomplished, the connection in the
bark has been re-established, and the organic nutritive matter can
be conveyed again into the basal parts of the tree and into the
roots. But if, for some reason or other, the union between the
wound calli is not completed, possibly because through too frequent
girdling the wound-calli have repeatedly been removed, the
available constructive substances below the girdle will sooner or
later become exhausted. The tree will become sickly; the roots
will no longer find the nourishment required for their existence;
consequently they can no longer absorb nor convey upwards an
adequate supply of water and salts for the wants of the tree. The
crown consequently suffers, and finally the tree will die. Under
such conditions, at what period the tree will begin to sicken,
must obviously depend entirely on the rapidity of its growth, on
the size of the reservoirs in its stem, and on the quantity of reserve
material accumulated in them. For that reason, young trees will
as a rule suffer sooner than old onelT~~

The experiment of girdling has a different result when carried
out on plants that contain medullary bast in the pith. They will
not suffer so easily, as by means of the bast in the pith, a
continuous transport of food substances to the base of the tree
can be maintained.

It requires but little imagination to see, that in trees without
bast in the pith, the transport of material to the base of the tree
will be disturbed by circular incisions, even though they have not
penetrated right through the cortex and the bast down to the
wood. The normal sap transport will be disturbed, even if only
some of the channels — for instance, those in the cortex and in the
oulcf layer of bast — have been severed. How far such an interrup-
tion of sonic of the conducting channel-, will 'disturb the vitality of
the tree depends on Various factor^ : lirstf \\ on the amount of matter

14 -

required by the root-system and the base of the tree; secondly,
-on the quantity of available reserve material ; thirdly, on the
quantity of organic matter, which can still be transported down-
Awards through the unsevered channels ; and fourthly, on the
rapidity with which the reproductive activity of the cambium can
provide a substitute for the severed channels on the spot operated
upon. Consequently it is impossible to predict off-hand the
number of channels in the bast and the cortex, the severance of
which will sooner or later kill the tree. This can be ascertained
•only by experiments suitable to each species of tree.

From the foregoing remarks, it is evident why, at the
commencement of this chapter, I expressed the opinion that
tapping incisions on rubber plants will result in a certain amount
of injury to the trees.

B. The Applicability of the Facts Enumerated to Rubber

Trees.

Is it, however, at all possible that these conclusions founded on
observations made on totally different species of trees, are applicable
to rubber plants ? May not their sap-circulation be subject to
totally different rules ? Do we not find in them quite a special
system of tissues, which is lacking in most other trees, and which is
diffused throughout the whole tree : the system of latex ducts ? Is
it not possible that this system takes an active part in the sap-trans-
port, and that the latex itself contains many important transportable
nutritive substances ? This theory is still very universally adopted
by many practical men. Botanical research has of course often
been occupied with the question. The results have been very
lucidly summed up by Kniep in a very excellent treatise, which
appeared not long ago,1 and in which also a number of new
and critical experiments on different kinds of laticiferous plants
have been communicated. On the basis of his own experiments
and those of his predecessors, Kniep arrives rightly at the
conclusion, that in all probability, latex is not a nutrient juice,
and that it is consequently of no importance as regards the
circulation of sap. What mostly interests us is the conclusion
at which Kniep has arrived by experiments in girdling the branches

1 Kniep, Hans. " Ueber die Bedeutung des Milchsafts der Pflanzen.
Flora." Vol. i, 94, 1905. Pp. 129, ff.

of a rubber tree — Ficus Elastica — that it is not possible by means
of those laticiferous vessels which are situated in pith devoid of bast
to effect a sap-transport across portions of branches, which have
been girdled down to the wood. However we must bear in mind,
that not all laticiferous plants need necessarily follow the same
rule. It will therefore be necessary to submit all the various kinds
of rubber plants to a series of special experiments. I take this
opportunity to mention that on Hevea my experiments of girdling
have had the same negative result, that Kniep obtained by his own
on Ficus. They will prove, that at least in the case of Hevea, all
the same rules for the transport and storage of sap in the stem
hold good as in the case of other trees.

C. Influence of Incisions on the Production of Latex in the

Bark.

In order to form a correct estimate of the suitability of any
tapping method, it is important to ascertain not only — as I pointed
out at the commencement of this chapter — to what extent tapping
will injure the vitality of the tree, but it is also necessary to
find out in what way it affects the renewal of bark and of
latex. The answer to the latter question will for the present
depend entirely on the solution of the former, and therefore the
solution of the first problem, being the fundamental one, is the
one which we must endeavour to obtain. We shall have no
difficulty in comprehending this, if we again make the experiment
of girdling the basis of our deliberations. Let us, therefore,
suppose, that cutting down to the wood, we have made a complete
girdle round a rubber tree, the pith of which is devoid of bast,
and that during this operation there has been an abundant How of
latex from the parts of the stem below the girdle. The important
questions for us to solve are, whether and in what manner girdling
will affect the re-filling of the partly drained laticiferous vessels
in the parts of the stem below the ring. Whether or no such
an influence will make itself felt, will depend solely on tin-
distribution of these vessels in the tissues of the tree. If the \ essels
only, or chiefly, occur in the cortex and the bast, the iiilluei). e
is a matter of course; if they are also t<> any extent situated in
the pith, an influence on the formation of latex in the tubes of
the cortex and of tin- bast belmv the girdle i> only then a matter of

course if these laticiferous vessels do not communicate right
through the wood into those of the pith. As, for instance, the
laticiferous vessels of tappable Hevea trees are diffused through-
out the cortex and the bast (compare the anatomical statements
further on), we can with regard to Hevea answer the first question
in the affirmative, and must admit, that girdling has an influence
onihe_cefilling of the vessels_below_th£_girdle.

I now turn to the second question: In what way can girdling
affect the renewal of latex ? It is not difficult to answer. Jf_
latex be produced only in the Ieave3^th^_d£scending^curjeftt of
latex cannot flow acrosS-the girdle towardsthe

b^ase of the tree. But if latex is produced in the stem, then, as
we have already seen, the downward transport of food supplies
becomes entirely suspended by the girdling. In the former case,
a refilling of the latex tubes below the girdle will be practically
impossible, as long as the girdle has not been bridged over by
callus.

We have every reason to assume that latex is produced, not
only in the leaves, but also, or almost entirely, in the stem.2
Some extremely important and interesting observations made in
Ceylon and Singapore with regard to the renewal of latex in
repeatedly tapped leafless trunks of old Hevea trees, for instance,
admit of no other interpretation.3 But if latex is produced_in
the stem, which isjujidiiubledljL_thjLcase, the nutritive substances
required for this purpose must__exist in thg__stem_ in sufficient
quantities.. _ If there is a deficiency of them, the_£enewal of latex
jnust necessarily suffer, the laticiferous vessels cannot Be

latex, and the supplementary latex may

possibly deteriorate in quality as compared with the original. We
have already seen, that after a complete girdling of a tree a
deficiency of nutritive substances must sooner or later make itself
felt in the stem below the girdle. The universal injury which

- None of the observations can force us to acquiesce in the
supposition, occasionally laid down, that latex is produced only in the
leaves.

s Compare for instance, J. C. Willis, M. K. Bamber, E. B. Denham.
"Rubber in the East." Peradeniya Manuals of Botany, etc., No. I.
Colombo 1906. Pages 25, ff.

H. N. Ridley and R. Derry. Second Annual report on the experi-
mental tapping of Para rubber trees in the Botanic Gardens, Singapore,
for tlie year 1905 (1907) Pages 24 ff.

the tree thus suffers, must necessarily extend to the quantity and
quality of the supplementary latex.

I have already pointed out, that under certain circumstances,
even incomplete girdling incisions, which only interrupt the
continuity of the cortex and of the outer layer of bast, may sooner
or later have a deleterious effect on the tree, on account of the
partial interruption of the circulation of nutritive substances.
If such an injury occurs, it is obvious, for reasons given above,
that it will not be without great influence on the renewal of latex
below the spot operated upon. It will have an influence on the
reproduction, all the greater the more latex has exuded, and
will therefore have to be replaced. A sufficient re-flow of latex
through the few vessels that may possibly still remain intact in
the inner bast, will be all the more impossible the younger and
more undeveloped are these laticiferous vessels.

In summing up all we have been considering in this chapter,
based as it is on well-known physiological data, I think we can
form the following conclusion, that in rubber trees (as in other
trees), cuts made very deep in the cortex and in the bast, are apt,
sooner or later, to disturb greatly some very important vital
functions of the tree, and consequently retard below the girdle
the renewal of cortex and of the latex that has exuded ; all the more
the deeper and more extensive these cuts are, and the longer the
period is, which will be required for the restoration of the severed
parts, because the reservoirs below the girdle will become
exhausted and a scarcity of food must occur in some parts of the
tree. The younger the tree, the sooner the injury will be
noticeable.

D. Problems for my Experiments.

How can we utilise this conclusion, in order to determine the
value of the various tapping methods ? Does tapping really
interfere with the vitality of the tree so much as, sooner or later,
to damage it seriously, and hinder the renewal of latex of good
quality? In order to decide these questions, it will IK- necessary
firstly to glance at the anatomical structure of the Hevc-a tree. ;m<l
secondly, to consider the demands made in actual practice on the
tapping cuts, so that a sufficiently remunerative yield of latex
can be obtained.

As regards the anatomy of the Mem o| Ile\e,i, it will lie

2

— i8 -

sufficient to draw attention to the following facts observed by
myself : if young trees are examined, one to three years old, it
will be found that the interior of the stem contains pith consisting
of thin-walled cells. Fibres of bast are completely wanting in
the pith. Some isolated, inter-communicating laticiferous vessels
run through the periphery of the pith.^ The pith, rich in starch,
is surrounded by dense wood. The living cells of the wood
are so rich in starch, tha(t a solution of iodine in diluted
alcohol will colour the whole body of wood an intensely dark blue.
On the outer surface of the wood, the creative tissue, the cambium,
is found, through the activity of which the tree grows in girth.
By division, it forms cells towards the interior, that enlarge the
wooden ring, and others towards the exterior, that thicken the
bast. Outside the cambium the bast is situated. In this a number
of laticiferous vessels are diffused, which like those in the pith, are
parallel to the axis of the tree and united by numerous cross-
connections. They, as well as the other cellular tissues of the bast,
are continuously reproduced by the cambium. Outside the bast,
last of all is the cortex. In it as well isolated laticiferous vessels
occur. The greatest amount of latex, however, is contained in
the laticiferous vessels, which are situated in the parts of the
bast, that adjoin the wood, and are still young. If we examine the
young green twigs of these trees, in which lignification has not
yet begun, we perceive that the medullary and cortical laticiferous
tissues, as well as those of the bast, are here and there united by
cross-connections, especially in all those places where a leaf or a
side branch emerges, namely at the nodes. But these connections
are not found in those branches, in which an unbroken ring of
wood surrounds the pith.

Older trees, which are what we have to consider for tapping,
do not differ much anatomically from younger ones. However,
I have made one significant observation, namely, that medullary
laticiferous vessels seem to have lost all importance, and have
become quite valueless in older trees. Their walls are of a
brownish colour, so are their contents; in many cases the vessels
have been compressed by the adjoining pith-cells. Naturally all

4 Miss A. Calvert has already described correctly the distribution
of laticiferous vessels in -the stem of Hevea trees. Vide her short treatise:
"The laticiferous tissue in the stem of Hevea Brasiliensis. Annals of Botany."
Vol. I. 1887-88. Page 75.

— i9 —

transverse connections between the medullary laticiferous vessels
and those of the bast are non-existent in trees of such dimensions.
This anatomical discovery of the obliteration of the medullary
laticiferous vessels, accords with the observation, that if green
unlignified branches are cut through, there will be a small flow
of milk from the pith, but not in well-lignified stems. It is note-
worthy from an anatomical point of view, that in older trees the
layer of bast has been greatly thickened through the activity
of the cambium, and consequently the laticiferous system contained
in the bast has also greatly increased in size.

Therefore, as the laticiferous vessels are situated chiefly in
the bast of the tree, and as the yield of latex is the greater the
younger the parts of the bast are in which they occur, it is surely
right to demand in practise, that tapping should penetrate to the
inner parts of the bast in order to ensure a sufficient flow of latex.
However, it must neither reach nor cut through the cambium, as
then the creative activity of the cambium would be too much
affected. In order to satisfy all these demands, a large variety
of tapping knives have, as we know, been invented. The labourer,
who uses one of these instruments, can without difficulty make his
incisions sufficiently deep, and yet not so deep as to injure the
cambium. Though it is true, that from even a small incision a
certain quantity of milk will exude, on account of the pressure
on the latex in the vessels, the quantity would be much too small
to be turned to account. Consequently we are induced to make
deep cuts into the stem, and not only one, but several cuts
simultaneously and at some distance apart, above and also along-
side of one another. These cuts are made on the stem in an
oblique direction, not vertically, as by such incisions only a few
of those laticiferous vessels would be severed, that run in a
longitudinal direction ; nor horizontally, as in that case the latex,
as it exudes, would not flow well, nor be easy to collect. It is
further necessary to make repeated fresh incisions after intervals
of one or two days, and these in close proximity to the old ones,
in order to draw from the tree the desired quantity of latex. It
is a very strange fact, the nature of which is not yet clearly
understood,5 and which seems to have been first discovered by

•' To me it seems very probable that this so-called wound response
is based on the same principle as the so-called blerdin- pressure, which
is noticeable as the result of wounds on a stem. But it is not the

— 20 —

Willis and Parkin, that the latex will only begin to flow freely
from incisions that are made one or a few days after the first
incisions.

The following process seems to be the basis for all tapping-
methods at present in use. A number of shorter or longer oblique
incisions are made in the stem of the tree, each a fair distance
above the other, and at intervals of one or more days, small strips
of bark are pared off with the tapping knife from the lower edge
of all the tapping incisions and along their whole length. This
process is repeated, till eventually the whole of the cortex and
almost all the bast has been pared off down to each next lower
incision. It is regarded as a matter of great importance, that
each time a very narrow strip of bark only should be removed,
so that it should take as long as possible to complete the entire
removal of the cortex, and for the tapping period to come to an
end. In order to prolong the time, and to spare and preserve as
much bark as possible, a favourable view has been taken of a
suggestion, which has been adopted in practice on many estates,
to make the incisions with the knife less deep, and at repeated
tappings, not to use the knife each time, but alternately the knife
and another instrument invented for the purpose, the pricker.
This pricker is a small star-shaped wheel with sharp teeth. It is
applied on the inner edge of the last incision made by the knife.
By moving it with an appreciable pressure along the whole length
of the tapping surface, those laticiferous vessels are severed that
are situated in the inner parts of the bast, and which have become
exposed by the last incision; and by this process the greatest
possible drainage of all vessels is obtained. The pricker should
penetrate as far as the cambium, but must not cause any injury
to this creative tissue. It seems that there is still a great diversity
of opinion as regards the advantages of the use of the pricker.
I shall refer to it again.

Two facts are thus characteristic of almost all tapping methods
in vogue : firstly, the entire severance by oblique cuts of extensive
areas of cortex and bast. The result of this severance is an
interruption in the stem of numerous channels for organic
substances. Secondly, the gradual removal of very large surfaces

question here of root-pressure, but of fluid secretions of living cells
in the neighbourhood of the wound. Compare L. Jost, Pflanzen-
physiologie. G. Fischer, Jena, 2nd ed. Pages 64, ff.

2 1

of cortex and bast, together with the extraction of large quantities
of latex. This necessitates an extremely extensive renewal of bast
and latex in the stem, for which purpose a large extra expenditure
of organic substances is required. These substances will have
to be obtained all the more exclusively from the reservoirs in the
stem, the more the downward current of food supplies from the
crown has been checked by tapping the tree. The expenditure of
material, as compared with a tree in its normal condition, is all
the more increased, in that the intensity of respiration is far
greater at any wounded parts of a plant, than at the uninjured
ones.

I think all these facts and considerations demonstrate with
sufficient clearness the necessity for investigating the influence
which the various tapping methods exercise on the distribution
of sap in the stem, and for ascertaining how far tapping
injures the tree by checking the downward current of sap.
It is only by such investigations that we can in time solve the
extremely important question, how much nutritive substance must
be present in the stem below and within the wound in order to
provide not only for the renewal of the removed bast, but also for
respiration, for the continuation of the normal growth in girth, for
the continued development of the root-system, as well as for the
reproduction of latex in its original quantity and quality. It is
conceivable and even probable, that a deterioration of the renewed
latex begins to show itself even before all the reserve material in
the reservoirs has been exhausted, in fact as soon as the growing
tissues completely absorb and utilise the reserve.

The objection might be raised, whether there is still any need
for such investigations, whether the experience gained in practice
will not yield sufficient information as to which of the tapping
methods injure the tree and will in time cause a deterioration of
the latex. The answer to this must be; firstly, that the views of
planters on the value of the various tapping methods differ very
much and contradict one another; secondly, that the injun. •-
resulting from bad tapping systems need not necessarily be very
apparent till after the lapse of several years. I shall discuss this
more in detail further on. It is against a fate of this sort that \\
must as much as possihl • guard rubber plantations by invrMi^.i-
systematically conducted. For of \\hat use' are estates, \\liich
s during a period of four to six years yi.-ld plentifully, but

— 22 —

must then lie fallow from exhaustion for years. Furthermore, it
is the duty of scientific research, based on well-established facts, to
lend a helping hand, when the experience of practical men is at
variance.

These were the ideas that guided me in my experiments. I
had to begin with an investigation of the influence exercised by
ordinary girdling on the transport of sap in the stem of Hevea,
and in connection with this, I had to compare the changes in
the distribution of sap in the stem after the tree had been tapped
in accordance with the various tapping systems in vogue. For
my purpose it was sufficient to ascertain the distribution of starch,
formed from organic material assimilated in the leaves and
transported in the form of reducing sugar6 through the channels
of the stem, and which chiefly fills the stem reservoirs. It requires
very little trouble to prove its existence. It is well-known that
the so-called iodine test is sufficient. When treated with a
solution of iodine in diluted alcohol the starch-grains rapidly turn
blue. If during these experiments, the starch has disappeared
from tissues, in which its existence had been already proved, there
are two alternatives, either it has become soluble and in this,
condition has remained in the tissues, or it has been conveyed
where it was required and has been utilized. If starch has been
dissolved, it is easy to prove the product of solution, reducing
sugar, by a treatment with Fehling's Solution. Other substances
besides starch and reducing sugar were not taken into considera-
tion at the investigation. (Whether it is desirable, or not, to.
include other substances, such as albumen and ammides, in our
research for the purpose of determining the value of the various,
tapping systems, time alone will enable us to decide.

b Reduzierende Zitcker must be translated " reducing sugar." It
is a more comprehensive term than glucose. It includes glucose, cevulose.
grape sugar, and fruit sugar, but not cane sugar — -in fact any sugar that
reduces Fehling's solution. — Tr.

PART II.
MY EXPERIMENTS.

A. Influence of Girdling on the Distribution and Circulation
of Sap in the Stem of Hevea.

I considered it sufficient to make these experiments on young
trees. More mature ones I could and would not sacrifice for
the purpose, had I done so, I am sure that the results obtained
would not have been different. My sole purpose was to ascertain
whether girdling has the same effect on the Hevea tree as it has
on other trees. As we know by frequent experiments, that other
kinds of trees are affected by this operation, no matter whether
they are old or young, we are surely right in assuming, that this
is also the case with old Hevea trees, if young Hevea trees arei
affected.

In my first experiments I made use of three yearling plants,
the height of which was 1,8 m., and which had been raised from
seed in the Large Botanic Garden. They were girdled in the
lower lignified part of the stem, 50 cm. above the ground. The
length of the removed ring of bark was 3 to 4 cm. Before
girdling them, the saplings were 3,5 to 4 cm. in girth just below
the girdle. The experiment commenced on December 22nd, 1907.
One of the plants was cut down for examination on February
i ith, 1908, that is after 51 days. The leaves were fresh, the crown
had continued to grow, but no new branches had been formed
below the girdle. The circumference of the stem above the
girdle was now 5,2 to 5,8 cm.; below it was the same as before,
3,5 to 4 cm. On the upper edge of the wound, pointing down
wards, a thin pad of callus had been formed. Above the girdle,
as far as the crown, I found much starch in wood, pith and bark.
It was especially abundant in the tissues above thr in< i^ion. Only

23

- 24 -

the pad of callus on the upper edge of the wound, was, curiously
•enough, completely free from starch. Of reducing sugar, I found
no greater quantity here than elsewhere in the bark. Below the
upper cut, however, down to the base of the tree, starch was
completely absent in all the tissues of the stem. Reducing
sugar also was almost completely absent.

The second plant was cut down eight days later. Its
condition with regard to the distribution of starch, corresponded
completely with that of the first specimen, though 2,5 below the
girdle, two young branches, with four leaves each had developed.

The third plant was left till the middle of March. Its
examination gave similar results.

It is evident from this experiment, that in consequence of
girdling, the circulation of sap in the stem had been completely
or almost completely checked, and that after a short time only,
the reservoirs in the stem were completely emptied. Outwardly
no damage to the trees was visible. Probably they would for quite
a long time have kept up in growth with the other trees, because
a long period must elapse before the want of food in the root-
system, and the retardation in its growth, show themselves in the
condition of the crown. Had, however, the latex been extracted
from the basal parts of the stem, I feel convinced, that it would
not have been renewed in its original quality and quantity, if
the tree had been left growing.

A plant, kept for comparison, which had not been girdled,
but was under observation, contained an abundant quantity of
starch in all parts of the stem down to its base.

The experiment was repeated in the following manner on
three bigger and thicker plants, two or three years old, their
height being about 2 to 3 m. I had one of these doubly girdled,
the rings were cut in the middle of the stem, at a distance of
about 50 to 75 cm. from each other. In the case of the other two
trees, I did not have circular incisions made on the upper wound,
but incisions extending only over half the circumference of the
tree. A square of bark from half to two-thirds of the circum-
ference iof the plant was then removed, so that on the upper wound,
a bridge of bark was preserved. The lower girdling was complete.
On all three plants I had the wound embedded in soil and
coconut fibre, by which the wood was fairly well protected
against desiccation. The plants were girdled on December 3Oth,

2 ^

1907. I purposely made the examination very late, that is, as late
.as April i6th, 1908. The doubly girdled tree contained an
abundance of starch in all parts of the stem above the upper
ring ; the callus only was, again, free from starch. Below the
upper ring, however, down to the base of the tree, reducing sugar
and starch were wanting, save in the innermost layers of wood.
Here was still a considerable quantity of starch. Above the
upper edge of the incision, a large number of roots had been,
formed on the upper and lower wounds, but a greater number
and longer ones on the upper than on the lower, apparently
because there was not so much food available for the lower one.
This plant is of special interest as compared with the younger experi-
mental plants, previously under our observation, because it shows
that the process of draining the reservoirs in the stem will be the
slower, the more extensive they are. While in the case of the
slender yearling, all starch disappeared from the stem after a
period of only 51 days, the thicker, three-year-old plant, after
three-and-a-half months, still contained starch in the innermost
zones of its wood. From this it is also evident, that the drain of
starch evidently starts from the bark.

The two plants with the bridge of bark on the upper wound,
presented the same appearance below the lower incision as No.
I., and also above the upper incision. But it stands to reason,
that the conditions between the two wounds were somewhat
different. For by means of the bridge of bark on the upper one,
it had been possible to continue the downward current of sap.
On the upper wound itself, starch and reducing sugar were almost
completely absent from the wood, that had been formed prior to
the operation. On the other hand, starch was abundant in the
newly formed wood inside the bridge of bark. And from the
ligneous part of this bridge, some starch, though but a small
quantity, had penetrated into the immediately adjacent old wood.
Below the upper wound down to the lower one, starch was again
present in all layers of the stem. It is impossible to draw any
conclusions from this circumstance with regard to the quantity
of sap that can be transported across the bridge of bark in .1
basal direction, as in every case, the- lower girdling had caused
an accumulation. Roots had Ixvn formed cliii-lly on the upprr
wound, only very few on tin- Lower "nc.

The conclusions to !>;• drawn from all these experiments i an IK-

— 26 —

summed up as follows : Corresponding with the absence of medul-
lary bast , a severance of the bast and the cortex will completely
interrupt the downward current of organic food material, so that
the reservoirs in the stem below the place of severance will, in
the case of young trees, be very soon emptied, in that of older
ones, more slowly. The result of this will be that a deficiency of
food will sooner or later occur in the base of the tree.

It would ihave been of great interest, not only for our
immediate purpose, but also in its relation to the tapping problem,
to ascertain by experiment, how rapidly the reservoirs which had
been emptied completely by girdling, would be refilled, when
the connections between the severed portions of the bark have
been re-established, as for instance, by the joining together of
the wound-calli. Such experiments would, however, have required
more trees for experimental purposes and more time than I had
at my disposal.

B. Influence of the Tapping Incisions on the Distribution and
Circulation of Sap in the Stem of Hevea.

In order to be able to compare in the easiest possible manner,
the influence exercised on the circulation of sap 'by the various
tapping cuts, with that of complete girdling, we must first consider
those tapping systems in which the rectilinear connection of the
channels for the organic substances is interrupted round the
whole girth of the stem, as in the case of girdling. These systems
only differ essentially from the ordinary method of girdling by
permitting a circulation of sap in an oblique direction, and also
because possibly the innermost channels in the bast, the youngest
and those nearest the cambium, can still be utilised for conveying
feed. Piobably the simplest of these systems is the English full
spiral system. It was very much in vogue some time ago, and
probably is still very popular. [The full-spiral system was recom-
mended in Ceylon at one time, and experiments were made at the
Heneratgoda Government plantation; but the recommendation
was never widely adopted, either in Ceylon or the Malay
Peninsula, and was speedily abandoned. — Tr.] A spiral curve is
cut in a slanting direction in the bark, beginning at about the
height of a man, and continuing down to the base of the stem.
The incision is carried one and a half to three times or more

round the stem. Naturally its direction is less sloping the
more often it envelopes the stem. By enlarging the wound at
intervals of a few days in the manner above indicated, the whole
bark of the stem will in time be removed. Of course it was
desirable in my experiments to have the tapping operation
performed in the customary manner by trained workmen.

Mr. Pit was kind enough to instruct his men accordingly. In
the first instance he put at my ^disposal a He'vea tree, eight
years old, that had never been tapped. At the height of, say
a man's chest, the girth of the tree was 50 cm. Tapping began on
November 8th, 1907. From the height of 1,28 cm, the incision was
carried one and a half times round the tree in a basal direction.
A distance of 50 to 52 cm. was left between the spiral curves.
Details of the manner of tapping can be seen on the accompanying
diagram. (Compare diagram 2.) It represents the bark of the
tree, as it would appear to the eye, reduced to one-tenth of its
size, if the cylinder of bark were cut open longitudinally and spread
out flat. Tapping was performed daily, alternately with the
Bowman parer and the Bowman pricker. Of course I ascertained
frequently, that the tapping cuts were properly executed. Tapping
was continued up to February loth, 1908. On February nth, the
tree was cut down for examination.

Before I communicate the result, I must refer briefly to the
examination of small pieces of wood and bark, made at various
times during the tapping period. For we derive from it some
interesting information with regard to the changes in the distribu-
tion of organic substances occasioned by tapping.

On December I5th, bits of bark, 5 cm long, were excised
from the tree for the first time, that is, 36 to 37 days after the

beginning of tapping, one bit (a'l, from
just above the incision. 10 cm from its upper
end, another (b), in a vertical line below (a),
just undrr the wound (Compare diagram
i), a third, (c), from the bark on the
opposite side of the stem, 100 cm above the
incision. Starch was found only in (c),
but not in (a) or (b). By treating with
Frhling's Solution, no difference in the
quantity of reducing sugar contained in (a),
(b) and (c) was apparent.

Diagram I.

28 -

On December 22nd, pieces of bark, (a) and (c) were again
•cut from similar places, and also a small piece of bark from the
wound near (a), (c) again contained a quantity of starch, but
(a), even at a distance of 10 cm from the wound, contained none,
nor did the bark on the wound.

I have also taken bits of bark from similar places on another
Hevea tree, eight years old, that had been tapped for a fairly
long period, and had been thrown down by a storm, on December
I2th, 1907, and have examined them for starch. The tapping
liad been performed on the half spiral system, so Mr. Pit said,
and had been continued from April to June, and from August
to October, 1907. Starch was completely wanting in (a) and (b),
while it was abundant in (c).

From these observations it is evident that soon after the
commencement of tapping, starch disappears from those parts of
the bark which are next to the cuts, not only below, but also
.above them, and that after the cessation of tapping, some interval
•of time must elapse before it can be reproduced even above the
incision. In the case of the fallen tree, for instance, one and a
half months had not sufficed to reproduce starch above the
wound. Evidently the starch in the neighbourhood of the wound
is claimed by the vigorous creative activity, which during the
period of tapping and for some time after, is at work in the
cambium below the wound.

These discoveries prove at the same time, that contrary to
my first impression, the examination of small pieces of bark does
not enable us to draw conclusions sufficiently as regards the
influence of tapping on the distribution and circulation of sap
in the stem.

For that purpose, it is on the contrary necessary, to sacrifice
the whole tree, at least for the present, till we have more data
on which to carry out less disastrous methods of investigation.

For this reason I saw myself faced by the necessity, of
having my experimental tree, that had been tapped on the full
spiral system, felled on February nth, that is after 96 days of
tapping, and long before the whole bark had been removed.
The wound was as yet only 12 cm broad. (Compare diagram
2.) The stem was cut into sections with a saw, after which parings
of the bark were systematically examined for starch and reducing
sugar. The wood also was at first examined in thin sections

— 29 —

Bunder the microscope, till the idea occurred to me to stain the
whole transverse section of the wood with a solution of iodine.
By this process it was very soon possible to obtain information
as to the distribution of starch in the wood : the starch-containing"
wood turned a blue-black ; that containing none, a yellow-
brown colour. I can recommend this very simple method to all
who feel inclined to continue research in the direction I have
indicated.

The result of the examination was most interesting. I begin
with the bark.7 Above the cut, starch was abundant, more so
than higher up on the stem. Only quite close to and above the cut
in a zone 5 cm wide was it in small quantity. The same was the
case beside the upper end of the wound. How starch is other-
wise distributed in the basal parts of the stem, will be seen best
from the diagram, in which I have set forth my discoveries
according to very exact measurements. Wherever the organic
substances, uninfluenced by the tapping, had been able to descend
vertically, quite as much starch was found as above the upper
spiral curve. Below this curve, however, that is, wherever the
organic substances had been forced to move sideways or obliquely,
a considerable decrease in the quantity of starch, commencing from
the upper end of the tapping cut, was very soon noticeable.
However, the existence of starch could still be proved in the
spiral strip of bark between the wounds, at a distance of half
the tree's circumference from the upper end of the incision
(measured parallel with the wound). Starch was com-
pletely absent from the other parts of cortex and
bast at the stem's base. By a treatment with Fehling's
Solution there was no difference noticeable between the reducing
sugar-forming property of the bark that contained starch, and
that which contained none.

The distribution of starch in the bark corresponded entirely
with that in the outer layers of wood : wherever starch was
entirely absent from the bark, or present only in a small quantity
the same condition existed in the outer, 2 cm thick, layers of wood.
Right at the upper end of the incision in a transverse sect inn
marked (a) in diagram 2.), starch, as in the case of the hark,

~( By bark I mean hen- as well as on the |>re<eeilin- pa;;e. \vhirh
I daresay has already been noticed, bark in the ordinary sense <>t tin-
word, and bast.

- 3° -

was absent only from that part of the wood just below the wound.
In a transverse section, marked (b), it was not only absent
below the tapping spot, but also below a piece of the remaining

Diagram II.

.bark, and finally at (c) in an unbroken ring of wood, 2 cm wide.
The inner parts of the wood, however, still contained abundant
starch, penetrating into the pith. Nor was it possible, by a treat-

• 31

ment with Fehling's Solution, to discover any considerable quantity
of reducing sugar in the zones of wood that were free from starch.

It is obvious at the first glance, that this result corresponds
almost completely with the one I had previously obtained on
girdled trees : the reserve material disappears below the spot
operated upon, and accumulates above it. A wound extending
over the entire circumference of the stem, has therefore the
same effect as the girdling, because the rectilinear connection of
the conducting channels in the bark has been interrupted and
because the circulation of organic nutrient substances in an oblique
direction proceeds too slowly to provide the food supply required
by the base of the tree.

Speaking generally, however, it seems to me that the conclu-
sion of most practical importance to us in our endeavour to
arrive at a decision on the various tapping methods is, that
after tapping qn the full spiral system, a sufficiency of the organic
nutrient substances that are necessary at the base of the tree for
the renewal of bark that has been removed, for the renewal
of the latex that has been extracted, for the normal growth in
girth of the tree, for the longitudinal growth of the roots and
for the respiration of the basal parts of the stem, cannot descend
there. The tree is therefore obliged to draw on the reserve
material from its reservoirs in the bark and wood. Tapping might
have been continued for quite a long time, as there was still a
sufficient quantity of tappable bark. During that time, the
reservoirs in the stem would certainly have been even more
completely emptied.

Another point of practical importance for the determination
of the value of the various tapping methods is the fact, that a
certain amount of sap transport, though a slow one, is quite
possible in an oblique direction. I shall refer to this later on.

Before doing so, however, I should like to report on a
second and final tapping experiment, which was commeneed
simultaneously with the first one. In this one, not the full .spiral
was adopted, but the half herring-bone system, which consists
in a number (six) of oblique cuts, one above the other.
The age of the tree was identical with that of the other
one, its girth was 50 cm. at the height of 1,00 in. Tin-
tapping cuts extended only over a quarter of the stem's
circumference. Their position on tin- tree, the distance between

— 32 —
them, etc., can be seen on diagram 3 (one-tenth of actual size).

Diagram III.

The operation of tapping was performed in the same manner*
as on the other tree. On three spots, the Bowman parer alone
was used (on the diagram evenly shaded), on the other three, the

• 33 -

Bowman parer and the Bowman pricker were used alternately
(on the diagram shaded by alternate lines and dotted lines). The
tapping period extended from November 8th to April nth. The
tree was then cut down and examined for starch and reducing
sugar with the following result : above the uppermost incision,
both bark and wood were very rich in starch. But there was
no trace of either reducing sugar or starch in a zone of bark
5 cm wide, immediately adjacent to the top end and the sides
of the tapping cut. Nor was starch or reducing sugar found in the
bridges of bark between the incisions ; on the other hand, starch
was everywhere present in the wood. Below the last and lowest
tapping spot, the presence of starch could be proved only in
the bark at a distance of 15 cm. from the last tapping wound.
On the incisions themselves, starch and reducing sugar were
absent both from the bark and from the outermost zones of wood,
1,5 to 2 cm thick. In all other parts of the tree there was
abundance of starch.

That starch was completely wanting in the bridges of bark
between the tapping spots, was probably due to the fact, that
owing to the transport in an oblique direction, not enough could
be substituted to replace the amount used up in this region.

This experiment teaches, that tapping cuts of this description
can at most have only a local influence on the descent of organic
food substances towards the base.

3

PART III.

INFERENCES AND FRESH PROBLEMS RESULTING
FROM MY EXPERIMENTS.

Having now obtained the proof, that in the case of some
tapping systems, namely, those which involve the extension of cuts
over the whole of the tree's circumference, an adequate supply of
organic food material for the wants of the base of the tree, cannot
be conveyed in a downward direction across the incisions, we must
now face the important question, whether the cuts will not in
time injure the tree seriously. As I have explained already,
injury is certain when the reservoirs at the base of the tree are
emptied, and cannot be replaced by a sufficient quantity of material
from the crown. It is quite impossible to obtain this fresh
supply, at least so long as the food channels are repeatedly
severed down to the cambium by repetitional tapping incisions,
that is, not before the end of each tapping period. If the tapping
period is a long one, and the tree comparatively young and
therefore still in the stage of rapid growth, it may be possible
that the reserve material will be completely exhausted even during
the first tapping period and that injury to the tree will be manifest,
for instance, in the deterioration in quality of the renewed latex.
Moreover, as I have already pointed out, we are at present still
quite ignorant, whether or not, the supplementary latex will be
poorer in quality, after a certain lack of food has really set in, even
though the reservoirs in the wood have been by no means
completely emptied. These problems, which are of the greatest
importance, in rubber cultivation, will at some future time require
thorough investigation on the lines I have indicated.

But even when the tapping period has come to an end, a
long time will elapse, and this we can maintain with certainty,

34

- 35 '

before a fresh supply of organic material can be conveyed across
the tapping spot, because a sufficient number of channels will
have to be reproduced by the cambium for this purpose.
Judging from observation, Hevea requires quite a long time for
this to be effected. Without special experiments, it is impossible
to determine, how long a period must elapse before the food
deficiency at the base of the tree can be made good by a fresh1
supply.

This extremely important question arose only after I had
ascertained the effect of incisions on the transport of nutrient
sap, and it was therefore only at the end of my stay in the tropics,
that I might have been able to investigate this subject had I had
some trees at my disposal which had been tapped for some time
previously. I feel sure that, on the lines I have indicated, I could
easily and rapidly have solved this question. It is certainly
important to strive to solve it as soon as possible.

Finally, it is important, not only to ascertain how soon the
transport of a certain amount of food material across the tapping
surface can again be proved to exist, but also, and chiefly, how soon
after the end of one tapping period it is possible to transport a
large enough quantity of material towards the base of the tree to
satisfy the probable very great need of food, which has arisen
in the bark during and after the tapping period, in consequence of
the necessary renewal of bark and latex, and also, how soon the
reservoirs of the tree can be refilled. I feel sure, that a long
time must elapse before the latter will be possible, and probably
this may not be till the reproductive activity has all but ceased its
work. This question, too, could be solved very rapidly by an
investigation of trees which had been tapped some length of time
previously. It is evident how necessary the refilling of the
reservoirs is, for the maintenance of the tree's life after a repetition
•of the tapping operation. If the reservoirs have not been refilled
completely, the tree will enter the second tapping period with
a much smaller quantity of reserve material than at the first one.
The result will necessarily be, that, at a second, third, or subsequent
tapping, the reserve material will have been completely exhausted,
that tin tree will be injured severely, and that tin- latex will
deteriorate considerably. I do not think it at all unlikely, on
the contrary it is very probable, that in thi^ manner, in. my bad
results can be accounted for, that pi, inters have had, with regard

- 36 -

to the falling off in quantity and quality of latex, after repeated
tapping operations, performed by very extensive incisions.

And lastly there is another question to which I must draw
attention, and which cropped up during my experiments, namely:
How long a time will elapse before starch can again be stored in
the bark that has been renewed on the tapping wounds. I have
never in my experiments noticed a storage of starch in bark
that had been renewed on the tapping spots, not even when a
sufficient quantity of food material had been procurable from
the neighbourhood, even when, after tapping operations, the bark
had had four to five months time to ripen. This accords with the
extraordinary fact, that starch is not stored in the calli formed
as the result of girdling, not even on the upper edge of the
incision, where organic material accumulates largely in the bark
next to the callus. The result of an examination of a very old
callus, is of great interest in this connection, because it proved
that a long period of time can elapse without any storage
of starch taking place in calli of this description. In the Large
Botanic Garden at Buitenzorg, I came across an 1 8-year-old
Hevea tree, the circumference of which was 75 cm, at the height
of a man's chest, and which had been tapped in February, 1907,
by a spiral curve cutting down to the wood. On the upper and
lower edges of the wound, calli had been formed. In a piece
of callus which I excised on December 22nd, I found no starch,
neither was there any in the new wood formed just beneath it,
while a quantity of starch was contained in the old bark just
above it. Nor did I find any special quantities of reducing sugar
in the callus. In order, therefore, to find out the condition of the
tree at the time when a second tapping period is to succeed the
first one, it would certainly be very important to ascertain whether
the newly-formed bark has regained its power of storing starch
or not.

It is evident that there are many important questions which
arise in connection with my experiments, and all of them questions
to which an answer can be found as rapidly and easily as possible
by an investigation of the distribution of material (of starch
especially), if only there are sufficient plants at one's disposal.
That was not so in my case. But I should imagine that in a
country, rich in rubber plantations, it ought not to be difficult to
induce planters to devote some trees to experimental purposes

- 37 —

of this kind. After all, it is in their own interest to find out which
of the tapping systems are advantageous, and which are not. I
feel convinced that more minute investigations in the directions
given, if entrusted to the right people, will very shortly increase
greatly our knowledge of the merits of the various tapping methods.
These investigations possess one advantage over many others,
in that they do not require new experiments, which might take up
years, but that they can be made on any plantations, where tapping
has been carried on for a longer or shorter period, so long as
the planter is in a position to furnish exact particulars as to the
dates of tapping, and the length and duration of the tapping
periods.

PART IV.

COMPARISONS BETWEEN MY OBSERVATIONS &
THE EXPERIENCES OF PRACTICAL PLANTERS.

All that now remains for me to do, is to investigate the
question, whether the results of my experiments — by no means
numerous and /very incomplete as they are — cannot explain some of
the experiences of planters, and whether they cannot throw light
on points on which these experiences are at variance. It is
certain that tapping methods are frequently adopted on estates,
by which, by means of spiral or other incisions, the rectilinear
connection of all fully developed channels in the cortex and in
the bast are severed. In Ceylon particularly, the full spiral
system was, at least some time ago, a very favourite one. (See
my previous note on page 26. It is evident that Dr. Fitting
obtained his Ceylon information just when the full-spiral system
was being advocated by a local authority who shortly after
abandoned it. — Tr.} It is a very remarkable fact, that more
than once, complaints have been made in the market about the
inferiority of the rubber, which had been collected during a
second or later tapping period. It appears that these yields
are richer in resin and poorer in caoutchouc than those of the
first tapping. This deterioration of rubber, which naturally
planters either do not like to admit, or refuse to admit at all;
may arise from various causes. It may be that the extracted
latex has been mixed with milk from trees that are too young;
another cause may be, that the planter has allowed one tapping
to follow too closely upon another. I am sure it would be worth
one's while to watch more carefully, whether tappings on the above-
named systems will not, /'// course of time, cause a deterioration of
latex, even if as long a time has been allowed to elapse between
each separate tapping period, as is deemed in theory sufficiently
long. That this supposition is not without foundation, is pointed
out by a statement made by Etherington,8 according to which the

* I Etherington. Experimental rubber tapping in Singapore Botanic
Gardens. Tropical Agriculturist. New ser. Vol. 28, 1907. Page 340.
Vide also Ridley, Second Annual Report on the experimental tapping of
Para rubber trees in the Botanic Gardens, Singapore, for the year 1905
(1907) Page 25.

38

— 39 -

yield of latex of trees tapped on the spiral system, in course of time,
actually becomes poorer in caoutchouc. Likewise it has been
noticed by many planters, who commenced tapping young trees
which had attained the necessary maturity, that the full spiral
system injures the trees in other ways. They have therefore,
adopted other methods. From a conversation I had with a planter
in the Southern Province of Ceylon, and in which we thoroughly
entered into all details, I gained the impression, that the damage
to the tree is chiefly noticeable in the growth of the crown and
foliage. But I did not gain a clear impression as to whether a
deterioration of latex had also been noticed.

In strange contrast to these observations, however, are the
experiences of other planters. For instance, I inspected a
plantation of old trees of large girth, the proprietor of which told
me, that on a system corresponding with the full spiral one, he
had for years gained abundant and excellent yields, without
noticing any damage to the trees, or deterioration of latex. I was
able to see for myself, that his biscuits were distinguished by great
resiliency and fine colour. Possibly this contradiction may be
explained by the fact, that in this case, the system was adopted
on old and not on young trees. Or the reason may be, that on this
estate, the intervals of rest between the tapping periods are
unusually prolonged. I regret not to have been sufficiently
informed on this point. As far as I could judge by the bark-scars,
this method had only commenced a few years previously, when
the trees were already well-established, while prior to that, the
incisions had not embraced so large an area. It would there-
fore be important to ascertain, whether older trees of larger
girth arc not much less easily affected by tapping methods that
interrupt the food channels on the whole circumference of the
stem, because they possess more extensive starch reservoirs in
the wood, and because their growth proceeds at a slower rate.
Perhaps a fresh supply of substances can be more rapidly obtained
from wide-spreading crowns. An investigation into this subject
is all the more advisable, because in this way sonic indication
may be gained, that a tapping method, which must in the case
of young trees be rejected as injurious, may without dis.uh .intake
be adopted for older trees.

PART V.

VALUE OF THE VARIOUS TAPPING METHODS IN
VOGUE JUDGED FROM THE POINTS OF VIEW-
ATTAINED,

In a recent book on the cultivation of Hevea, the author
advances the following maxim, by which to decide the value of
the various tapping methods : " The best method of tapping is
that which extracts the maximum amount of latex from the tree with
the removal of the minimum quantity of cortical tissue and without
damaging the thin layer of cambium cells."9 But judging from
my experimental results, I think the following addition, at least
in the case of young trees, should decidedly have been made :
And the best tapping method is, furthermore, one that checks the
transport of organic material in the bark towards the base of the
tree for the minimum length of time, with the minimum degree}
of intensity, which most confines this interruption to a local area,
and which consequently does not in course of time damage the
tree, nor injuriously affect the renewal of bark or latex.

From my observations, therefore, I consider it absolutely
necessary to condemn quite a number of tapping systems as
unsuitable for young plantations, where the trees have only just
arrived at tapping maturity. With regard to the future of the
plantation, it is necessary when tapping to remember as much as
possible, that trees, which at the commencement of the tapping
period were by no means large or thick, must become larger,
in order that their latex systems may develop and yield continu-
ously remunerative latex in large quantity. The advantages of
such a lenient treatment of young trees for the yield of future
years, certainly will outweigh greatly the advantages of a quick

9 H. Wright. " Hevea Brasiliensis or Para Rubber." 3d. edition.
London, 1908. Page 89.

40

yield, which after all, by reason of injury accruing to the tree,
may only be of short duration.

Judging from the results of my experiments, I feel bound, in
the case of young trees, to warn planters against the use of all those
tapping cuts by which the rectilinear connection of the vertical
channels for the circulation of organic substances in the cortex and
bast suffer a complete, or almost complete, interruption at any spot
between the crown and the base of the tree. I would also advise
them to abstain from all these methods, at least while we are quite
in the dark with regard to the length of time required after the
conclusion of the tapping period for the refilling of the reservoirs
in the stem below the tapping spot. But even after this point has
been cleared up, all those tapping cuts will always be preferable
which do not, even temporarily, subject the trees to any extensive
injury.

Therefore, in the case of young plantations, the first system
to be rejected is the spiral one.10 Just as impracticable are all
other methods which adopt the same principle as the spiral
incision : V-cuts, which leave no rectilinear strips of bark of
any great size on the tree, the double herring-bone incisions, that
cover the whole of the tree's circumference, two half herring-bone
incisions, each of which extends over half the tree's circum-
ference. Furthermore, I consider all those tapping methods
unsuitable, by means of which straight strips of bark are jat
first left between the incisions, which are, however, in the second
tapping period, following on the first one, completely removed
by a new system of incisions. It is on the contrary, absolutely
necessary, by means of old, uninjured bark, or at least by bark
that has not been tapped for a long time, to keep up a sufficiently
broad rectilinear connection between the crown and the base of
the tree, until the necessary number of new channels has been
formed in all parts of the bark which is being renewed on the
tapping spots, including therefore that beneath the very last
tapping incision; until it can be proved, that the new bark has

10 It is a matter of indifference, whether in adopting the spiral
cut, the bark of the tree is removed rapidly or slowly. The spiral curve
is not to be rejected, because by this method a ,^re .it t|uantity of bark-
is in course of time removed from the tree, but because it completely
destroys the food-channels. It set-ins to me necessary to lav stress on
this fact, because several competent authorities still seem undecided on this
point. Compare for instance, H. Wright, " I levea Hrasiliensis," | .ondon, ed. ;,
iooH. Pages 94 and 132.

cr
6

— 42

sufficiently " ripened " to carry on adequately the transport of
organic material, and until the reservoirs in the wood beneath it
have been refilled with starch. A long time, possibly one to two
years, will certainly be required for all these operations. This can
be ascertained easily by investigations.

As the flow of organic substances has been checked
completely in all those parts of the tree's circumference, in
which the vertical channels have been interrupted entirely by
tapping cuts, it is furthermore necessary to reject all those tapping
methods by which the rectilinear connecting channels between
the crown and base of the tree are either too few in number or
too narrow in width. For, on account of the extensive renewal
of bark and latex, the amount of material required in the base
of the tree has increased remarkably.

Lastly, it is advisable, judging from the results of my
experiments, to avoid all tapping methods, by which, although
stress is laid on the preservation of sufficiently large vertical
strips of bark, yet the incisions are made of such length, that
the organic nutrient and constructive substances within the tappin
system must travel too great a distance in an oblique or even
horizontal direction. For these substances, as I have previously
explained, circulate very slowly in an oblique direction.11 It
might thus happen, that & certain want of food might maker
itself felt in the portions of bark below the tapping incisions, and
that the renewal of latex might be impeded even during the
tapping period.

It" is 'most interesting to see how nearly the tapping methods of
the natives in the jungles of America, come up to many of these:
requirements, if they are rationally employed. Tapping is there-
performed by means of small axes, the blades of which are only
1,5 to 3 cm broad. Oblique cuts are made with them right
through the bark. Three or four of these incisions, 1,5 to 3 cm
wide, are made simultaneously and at an equal height, at a.
horizontal distance of 10 to 20 cm, from each other. They begin:
as high up on the stem as they can reach, and day by day they
make new cuts in a vertical line and at some distance below the-
old ones, down to the base of the tree. Then they begin agaia
at the top, in the spaces that were left in between. It is obvious

11 In an oblique upward direction the circulation will in all
probability be specially slow.

— 43 -

that by these incisions, vertical strips of bark are preserved for
quite a long period of time. I have not obtained information as
to how long the tree is rested after each tapping period.

For practical reasons, I do not believe that estates will
revert to a tapping system based on this procedure. It is not
very easy to spare the cambium by a method of this description,,
neither is it easy to collect the latex, nor does one succeed in
deriving the full benefit of the wound response, during the tapping^
operation, nor, finally, in milking the bark as completely, as in
practice one would like to do. I am rather of opinion, that estates
will have to keep to a system by which at short intervals narrow
strips of bark are again and again removed from the spots of
tapping. It will hardly be possible to raise any objections based
on physiological facts against this universally adopted method.

If now, after all these considerations, we pass in review the
various tapping systems, that in the course of years have been
recommended, we come to the conclusion that only very few of
them fulfil the requirements I have enumerated, and appear
suitable for young plantations. Only those remain for our con-
sideration, by which the last remaining straight strips of bark
are not removed sooner than during the third tapping period.
If in reviewing the value of the various tapping methods, we also
consider the demands made in practice, namely, that the latex
should run easily and be easy to collect, and the incisions easy to-
make, and that the flow of latex from the wound should have
full play, we have no difficulty in giving preference to the herring-
bone incision, as long as it embraces only a small part of the tree's
circumference. If the incision be extended over half the tree's,
circumference, too long a time would have to elapse after the end
of the first tapping period, before it would be possible to begin
with the second. If it be extended over a third of the circum-
ference, the. series of incisions would, during the second tapping,
hinder on one side the side-flow of organic food material towards
the cortical tissues, which have been renewed beneath the incisions-
made in the first tapping period. Everything, therefore, points
to the following: to extend the tapping system only over a
quarter of the tree's circumference, to tap a second quarter in
the second, and the remaining quarters in the third ami fourth
tapping periods.

We have still to consider whether preference should be gi\ en

— 44 —

to the full or half herring-bone incisions, and whether too great
an injury will not be caused to the tree, if as is the custom, all
oblique cuts are connected by \a vertical drainage canal. As
regards the first question, the V-shaped, herring-bone incision
has probably an advantage over the half herring-bone incision,
because in the case of the V-shaped incision, it is possible for
the organic food material to flow obliquely from both sides out
of the old bark, down into the V-shaped bridges of bark between
the incisions, which are disposed one above the other, and because
in this case it is only a question of short channels. In the case of
the half herring-bone incision, the downward flow can come only
from one side and the distance is double. I do not share the
doubts that have been expressed with regard to the vertical
drainage canal. I do not think that a canal of that description can
do much damage to the bark, provided it is not made either too
•deep or too wide.

And lastly, it will be necessary to discuss the important
question, whether or not the pricker should be used. This
instrument possesses undoubtedly certain advantages. For one
thing, the cuts with the knife need not be made so deep into the
inner cortex, and in consequence, a smaller amount of bark will
be removed, and secondly, it is not necessary to cut away strips
of bark so repeatedly, and the tapping period can therefore be
prolonged. But it would be a mistake to imagine, that the pricker
does not cut through all channels in the bark down to the cambium
on the entire tapping surface, just as deeper cuts with the knife
would, and that labourers, using this instrument, are not extremely
liable to injure the cambium.

But the question, whether the pricker is suitable, must be
decided by the way in which its use affects the renewal of bark.
If there is no difference in the results as compared with those
obtained by the deeper cuts with the knife, the pricker can be
used without hesitation. As, strange to say, no investigations
on this subject have so far been made, I ordered in the case of
the tree tapped on the herring-bone system, the knife only, and
the knife and the pricker combined, to be applied alternately to
the tapping-spots situated one above the other. I made a minute
anatomical examination of the bark, that had been renewed in
the course of four to five months. Wherever the pricker had not
been used, bark had been produced which did not differ from

- 45 —

the normal secondary bark containing laticiferous vessels. But the
sections made through the bark, on which the pricker had been
used, showed a very different picture. Wherever the teeth of
the pricker had penetrated to the neighbourhood of the cambium,
the latter had formed a new bark with many stone-cells, but
without, or almost without, laticiferous vessels. Where, however,
the teeth of the pricker had not penetrated through the
inner cortex, new bark had been formed containing laticiferous
vessels, that were arranged irregularly, or (as in the case of
normal secondary bark), arranged in rows. The entire surface
of the bark was uneven ; everywhere between the cuts of the
pricker the cortical tissue had bulged outwards. From this it
would appear that the bark on the tapping spots is renewed much
more evenly if the knife is used exclusively, than if knife and
pricker are used alternately. In the former case, therefore, the
bark ought to be much sooner ready for re-tapping than in the
latter. By making further observations and by comparing, under
the microscope, sections of the renewed bark after a longer
period of time than it was in my power to give, it will, I feel
sure, not be difficult to ascertain how much longer the latex
takes to ripen after the use of the pricker than after the use of
the knife, and whether the greater quantity of latex obtainable
by the use of the pricker, compensates for the longer resting-
period required before the commencement of another tapping
period. For this reason I feel justified in warning planters
against the use of the pricker. And this the more, as I have often
noticed on estates, that the teeth of the pricker had penetrated
into the wood. The pricker is evidently an instrument that is out
of place in rational estate cultivation. It would be better to make
the tapping cuts somewhat deeper and to remove a little more
cortex and bast.

PART VI.

SUGGESTIONS FOR RATIONAL TAPPING

METHODS.

According to my observations and the conclusions to be
•deduced therefrom, and also according to other experiences made
to date, I believe that in the case of young plantations and with
regard to their future condition, it will be best to perform the
tapping operations in the following manner :

Do not begin to tap the trees till they aresix to
•old^triaTTs.' till the~~ciHumterence of Tfie^tree~lsabout 50 cm_
at one metre above the ground"! Adopt Ihe^halfherring-bojie
incision as your tapping system, orTjetterstill, the full herring-
T3OTie7 the ^v^haped incision. The incisions must not be too
little vertical, as otherwise [Tie conveyance of sap from the sides
is rendered too difficult. An angk-of-sixtv degrees woujdjprobably
prove the best. The tapping system must only cover a vertical
.strip of bark, the breadth of which does not exceed a quarter
•of the tree's circumference. Make the upper incisions at about
the height of a man, by no means higher than where the tree
attains a circumference of 45 cm.12 Make the incisions one
.above the other in vertical distances of 30 to 35 cm. Tap daily,
•or every alternate day, with the knife only, and earlv_in the
morning.13 Impress on the workmen that the strips of bark they

12 Compare J. C. Willis and M. K. Bamber. " Tropical Agricul-
turist," Vol. 29, 1907. Pages 244, ff.

1S A circumstance which points to the morning as the best time,
is, that the diurnal period of expansion in girth attains its maximum in
the morning. The periodicity of expansion in girth in the case of trees
belonging to our latitude and to the tropics, has been discovered by
Gregor Kraus. (Ueber die tagliche Schwellungsperiode d. Pflanze.
Abhandlungen Naturf. Gesellsch. Halle. Vol. 15 and Annales d. jard.
bot., Buitenzorg, Vol. XII. 1895. Pages 210, ff.)

46

— 47

remoyein tapping" with the knife must bf ^ rmrrnw as possible,
and that they must not injure the cambium. It is necessary to
prolong theTtapping period as mucji__a^_possibj£J^-aJ_Jeaat_to_(3ve
or six months. During this tirn^ the whole of the bark between
the incisions may be removed. It is not possible to lay down a
general rule as to which season is best for tapping. That will
depend on the climate of each district. If the trees go through
a wintering stage, that is, if they shed their leaves, do not tap
during that particular season, which in the tropics is generally a
dry one. The rainy season is the most suitable one, especially the
beginning and the end of the rains. Nor is it possible to decide
off-hand, whether it is advisable to milk, in each tapping period,
all the bark on the strip which is being tapped, without an
interval of rest. It will certainly be possible to continue tapping
as long as the flow of latex does not appreciably diminish, and
its quality does not deteriorate. In order to come to a definite
decision on this point one should always only mix and further
prepare latex that has been collected from incisions on trees at
an equally advanced stage. I am of opinion that the mixing of
latex of different quality, for instance, that from young and from
old trees, or that from trees at different stages of tapping, should
be avoided most carefully. I am sure that a single or jrerjeated
_greater interval between the tapping^ of a tappin^_parinir|J rannni-
be harmful, but on the contrary, will prove beneficial Hence
I would deem it advantageous to_tap. for two or three naonths,-
and during this time, to remove at most the half of the strips
of bark Between two incisions ; after thatto__gaiise — for., one
to two months, and then to finish tappmgthe remainder of the
,strips^'ofJbark~Trr two to three months.

When the first tapping period is over, allow the tree a rest
of several (five to six) months. Begin the second period a
year later than the first. Tapping must now be performed on a
strip of bark extending over a quarter of the tree's circumference,
and situated on the opposite side of the stem and opposite
th • strip of the first period. The operation is the same as in the
first period. In the third period, which commences in the third
year, the strip of bark lying between I .md II must be t.ipp.'il.
and the last one in the fourth year. Then start again with tin-
first. As strip III immediately adjoins strip II, which has just
been tapped, it might be advisable to leave a narrow vertical

strip of bark, one to two cm wide intact, between II and III,
so that a certain downward sap-transport is still possible from
the leaves. If the half herring-bone system is adopted, it would
be possible to use the canals of the first and second tapping periods
as drainage canals for the latex when tapping the strips of bark
III and IV. Therefore only two such canals are required on the
stem. In that case it is, however, necessary to make the tapping
cuts of periods III and IV in an oblique direction opposite,
to those of periods I and II. It is impossible to decide off-hand,
whether, when tapping the previously tapped strips of bark for
a second time, it might not be advisable to make the cuts of the
tapping system in a contrary direction to those of the previous
one. Whether or not it is feasible with regard to the future life
of the tree, to commence the fifth tapping period a year after
the initiation of the fourth, should in my opinion be made to
depend on an investigation of the sap distribution in the stem.
It would be necessary to sacrifice two or three trees for this
purpose, and to get an expert botanist (probably at some experi-
mental station) to make an examination for the distribution of
starch in wood and bark on the tapping area. If the reservoirs
in wood and bark have been refilled, there can be no objection
to the continuation of tapping, provided that the latex exuding
during the fresh tapping period satisfies in quality and quantity
all fair demands. If, however, the quantity of reserve material
in the reservoirs of the stem proves to be as yet too small, it
will be for the expert to decide how long the tree must have
complete rest after the fourth tapping period. These examinations
ought to be repeated at least every four years, at the end of each
fourth tapping period.

If there are any trees on an estate, which for some reason
or other are to be removed, there is naturally nothing against
milking them as completely as possible on the full spiral system.

After three or four cycles of four tapping periods each have
gone by. without causing any deterioration in the latex, or injury
to the trees, one rnignt feel inclined to extend the tapping
incisions from a strip of bark measuring a fourth of the tree's
circumference, to be a broader one measuring a third of or half
the tree's circumference. Personally, for scientific reasons, I
would unquestionably consider it to be most advantageous, even
in the case of mature trees, to keep to the original tapping system,

- 49 -

and further for this reason, that every transition to a different
tapping system is accompanied by technical difficulties. I would
consider it a better idea to try the experiment of allowing the four
tapping periods of one cycle to follow each other more closely, so
that the whole cycle would not embrace as many as four, but
possibly only three or even only two years. But experiments of
this kind, or any other experiments with new and other tapping
methods, should never be undertaken without having an examina-
tion made from time to time as to their effect on the circulation
of sap in the stem and on the quantity of reserve material contained
in its reservoirs. I look upon this as one of the most important
means for arriving in course of time at rational tapping methods.

It is of course not excluded, on the contrary quite possible,
that an investigation of all the questions I was able to raise in
connection with my experiments, will further substantially increase
our knowledge of this very difficult subject, and that we shall
then succeed either in modifying my suggestions on this or that
point, or in establishing them still more firmly. It is, therefore,
a matter of urgency that these investigations should be undertaken
without further delay. I have already pointed out, that it is
merely a question of sufficient plant material to carry them out
in the shortest possible time.

The tapping method (the herring-bone incision on a quarter of
the tree's circumference), which I feel justified in recommending on
the basis of my experiments, is also the same to which Ridley,
in Singapore, recently tried to draw attention. It is a great
pleasure to me, that my views coincide unreservedly with the
opinions of one who is such an excellent authority in the province
of rubber research. This concurrence of views, is all the more
gratifying, as we seem to have arrived at our opinions by different
ways. Anothexjidvantagc of this method is, that it gives regular
occupation to the labour force year after year, and day by
dax without any7 very great interruptions. It may be possible,
at leasFin many districts, to distribute the time of the tapping
periods in such a manner over the different parts of the plant-
ation, that there is no month in the year in which lapping is
not carried on.

If anyone should consider it important that during each
tapping period, latex should be extracted from various parts of
the tree's circumference, and not from one continuous strip of

4

— So —

bark, extending over a quarter of the circumference, the following
method may without hesitation be substituted: Make oblique, or
V-shaped incisions along two strips of bark, that are exactly
opposite each other on the opposite sides of the stem, and the
width of each of which is an eighth of the tree's circumference.
Tapping has to be performed in exactly the same manner as in
the other method. During the second tapping period, tap two
strips of bark, each of which is an eighth of the tree's circum-
ference wide, and which are situated opposite each other and
exactly in the centre of the strips of bark that have so far remained
intact. In the third tapping period, tap two more strips of bark
situated opposite each other, that have before been left untapped;

and in the fourth, the remaining two.
(Compare diagram 4 for the trans-
verse section of the tree.) In the
fifth tapping period, start again with
the two strips of bark of the first
period. As regards the precaution-
ary measures that must be taken
in order to prevent an injury to the
trees, especially with reference to the
commencement of the fifth tapping
Diagram IV period, compare what I have said

about the other method. I consider

this method a very good one. Probably there are several reasons,
on account of which it is even better than that one, by which only
one strip of bark, a quarter of the tree's circumference wide, is
tapped.14

But we will have to consider whether this method can be
recommended for trees six to eight years old. For in their case
we have to reckon with a circumference of only 50 to 60 cm,
arid each of the two strips that are simultaneously tapped would
be only 6 to 7,5 cm wide.

Perhaps some planters will wonder that I do not enter into
some of those questions of detail, on the solution of which so much

14 The yield of latex gained by this method will probably be greater than
by the other one. According to Pit, the yield -per unit of bark excised is all
the greater, the smaller the wound-surface. (Compare Teysmannia, vol. 19,
1908. Pages 479, ff.) From this we would infer, that two small incisions, which
are situated on the stem some distance apart, yield more latex, than a contin-
uous one embracing the same area as the two small ones put together.

time and trouble are at present expended, for instance, whether it is
of greater advantage to tap daily or only every other day ; whether
downward incisions made from right to left yield more latex than
those from left to right ; whether it is better to make the drainage
canal in a straight line, or zigzag, etc. I must confess that I do
not look on any of these questions as of special importance.
It is impossible to decide them scientifically. And a decision
based on experiments would only be possible if these
experiments were not confined as heretofore to a few trees, but
extended to hundreds. It seems to me, however, that the solution
of these questions is more or less immaterial for the rational
working of an estate. It is much more important to proceed
rationally with regard to the larger issues. The small advantages,
that might be gained temporarily by the consideration of such
minor details, might be counter-balaced by small disadvantages
in a lesser yield, which would show themselves later on.

Finally, I should like to mention a point which has been,
forced on me by the results of my experiments. It refers to the
estimate of profits in opening up a new estate. My opinion is,
that one should never reckon on average higher yields than can
be expected by adopting the tapping methods I have recom-
mended, or similar ones.

1 S \\.irui.k, II. up in Printing Work ,

1858