586 THE TROPICAL 
THE FUNCTIONS OF RUBBER 
LATEX. 
The nature and fanctiona of latex in plants are diffi- 
cult problems. Very different Siig3;eations regarding the 
uses of latex have been defeudsd by different invesfci- 
pators on the basis of studies of different plant?. Tne 
first observer, acoording to the ladia-Itubber Jour- 
nal, compared them to the blood of animals, and des- 
cribed the globules of {',um as corpuscles, a hif^hly fanci- 
ful notion which later writers have so zealously dis- 
avowed that they have felt it necessary to deny any cir- 
culation at all. Some have held that the milk tubes 
are reservoirs for the storage of elaborated food 
materials, while others believe that kjtex is an excre- 
tory or waste product, even to the proteids, starch, and 
sugar with which the milky juice is commonly charged. 
Protection against insects and snails has also been 
urged as the funciion of latex. 0.ie of the most recent 
writers on the subject* reviews and dismisses all the 
previous suggestions apparently for the reason that 
none is of general validity, and, after detaling numer- 
ous observations of his own, comes to the following 
disappointing conclusion : — 
_ It seems impossible to discover what is their func- 
tion, or to ascertain if there is one function common to 
all laticiferous tubes until micochemicpl methods are 
' vastly improved, or until analyses of latex in its various 
stages are made." 
Obviously, however, there is no rtason why it must 
be believed that all the functions of all milk tubes are 
the same, or why one function should exclude another. 
That insects, such as leaf-cutting ants, should not be 
able to attack rubber trees because the gum would 
disab'e their mouth-parts might be an important 
advantage in Central America, bat would not explain 
rubber in African plants not subject to the depredations 
of these insects. The most that can be done is to 
learn the uses of latex in one plant at a time, without 
anxiety as to whether or not a general function for 
latex in all plants will be discovered. 
SEASONAL INFLUENCES ON HUBBEE LATBX. 
No theoretical consideration need interfere with the 
recognition of any relation which can be proved to eX' 
ist between the amount of latex or of rubber obtain- 
able from Oastilloa and the climatic conditions under 
which the trees are found. The most direct evi'ience 
of such climatic influence is to be found in the seasonal 
changes in the latex. Such differences in the 
rubber contents of the milk at different seasons had 
received little attention from recent writers, though it 
is not a new fact, since a detailed statement was 
published by Collins over thirty years ago. 
RUBBER LATEX IN DRY SEASONS. 
In Nicaragua it is found that although the hnle 
yields the juice at all seasons, the most fivourable 
season is April, when the old leaves begin to 
fall and the new ones appear. During the rainy 
season from lilay to September, the richness ot the 
jaije diininishes. Prom that time to January the 
rain diminishes and the milk increases in richness, 
and the tree prepares to floA^er. The fruit appears 
in IMarch, during which month and the succeeding 
one the milk is at its richest. The yield of caout- 
chouc contained in an equal quantity of milk would 
in April be 60 per cent more than in October. 
The increased richness of the milk in the dry season 
Bsems to be recognised in all districts where the dry 
season is long enough to permit the effect to become 
appreciated, but in localities where the dry weather in 
which tapping can be done is short there is at once lesa 
difference and leas opportunity for it to become 
evident. Where the dry season is long, as at La 
Zicnalpa, the flow of milk becomes small, and tapping 
is deferred until some rain has fallen, when the quan- 
tity and quality of the milk are both at their bes'. 
The popular idea is that as the dry season advances 
* Percy Groom on the Function of Laticiferous 
Tabes, " Annals of Bo'.any,', III. 157. 1889. 
AGRICULTURIST. [March 1, ldo4. 
the milk becdmes too thick to flow, and that during 
the rainy season it becomes too poor in rubber to pay 
for tapping. The fact that the latex becomes richer 
during the dry season does not prove, of course, that 
the additional percentage of rubber is a measure of 
protection against the dry weather. It may be that 
the rapid growth which goes on in the rainy season 
uses up the rubber, while the cessation of growth in 
Ihe dry season permits it to accumulate. This pos- 
sibility does not, however, exclude the other, but 
seems rather to strengthen it, since there are other 
reasons for believing that the possession of latex is an 
advantage in the straggle against drought. S veral 
such facts were noticed during a recent visit to Bouth- 
ern Mexico. 
WATER STORING AS A FUNCTION OF LATEX. 
The recognition of a relation between latex and dry 
weather has been hindered rather than helped by the 
attempt at framing a theory of the use of latex to the 
plant; but a few writers have appreciated such facts 
as the above, and have been inclined to look upon the 
storage of water as the long sought general function. 
The following extract affords an instance : — 
" It the formation of laticiferous tubes has been 
called forth in all plants po-isessing them to perform a 
common function, then I am i'lclined to think the idea 
of their serving as channels for holding water in 
reserve as one of the most plausible. Laticiferous 
plants are markedly characteristic of tropical regions, 
where transpiration is great. The development of 
a system of tubes running throughout the plant to 
be filled with water during the wet season, and then to 
be gradually drawn upon during times of drought, ia 
intelligible, 
" Warming, in a paper in the ' Botanioul Gazette ' 
for January 189'J, entitled 'Vegetation of Tropical 
America,' mentions lianas and other plants of tropical 
forest and scrub as often laticiferous, and says " Most 
likely latex serves several purooses, and one of them, 
I suppose, is to supply water to the leaves in time of 
need when transpiration becomes too profuse.' 
HEVBA TREES IN CEYLON. 
" Prom our experiments in Ceylon we found that the 
quantity of latex extractable fr<m incisions in the 
trunks of Hevea trees varied considerably with the 
time of the year, and seemed to depend la'gely upon 
the available moisture in the soil. After heavy rain 
the exuda'-ion of latex is mu3h more copious and 
thinner, looking as though the vessels had become 
surcharged with water. 
As the necessity for a reserve of water increased, 
the laticiferous system would tend to bsoome more 
extensive and mora intimately associated with the 
surrounding tissues. The p;enu8 Euphorbia chiefly 
inhabits dry regions and is one of the richest in latex. 
" Thl« view does not explain the proteid or slaxh 
grains of latex, yet I think it is one to be borne in 
mind in studying the role of la'ex in plan's, and 
hitherto it has in the main been disregarded. It latex 
does serve as a water reserve, then perhaps it ia chiefly 
valuable for the growing organs." f 
SIGNIFICANCE OP MULTIPLE TAPPING. 
The latex problem aiquires an interest from the 
recent demonstiation that Hevea, at hast, contiouea 
not only to yield milk by the daily renewal of the 
wounds, but that the quantity aituilly increases for 
several days. This might seem to favour the idea that 
the latex has a nutritive function, the alditional 
quantities being assembled, as it were, to repair the 
injury. On the other hand, the supposition that the 
rubber hinders evaporation would also work equally 
well, and affords the additional suggestion thai the 
greater evaporation from the wound may assist in col- 
lecting the rubber about it, the yield increasing as the 
widening of the wound increises the surface of 
evaporation until the available supply of latex has bsen 
depleted. 
t Parkin, "Ann" XIV. „ 212-213,1900 ~ 
