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from branching by being planted too close together. The ques- 
tion of how close or how far apart the trees should be planted is 
one that has had a great deal of attention and is one of vital 
importance. 
In considering the problem of how many trees it is best to 
plant to the acre, it is necessary to consider condi- 
Hon' Close tions as they are likely to exist in the future. In 
to Plant. planting rubber for profit, it is the percentage of 
profit on the capital invested which determines its 
value as an investment rather than the gross earnings or profit 
per tree or per acre, or the total output of the plantation. 
If we let 
N. Represent the acreage planted. 
X. Represent the number of trees per acre. 
T. Represent number of times a tree is tapped per year. 
C. Represent capital invested. 
N. Represent the number of trees per day one man can tap. 
y. Represent yield per tree per day's cutting. 
p. Represent price per pound of rubber. 
L. Represent days wage per laborer. 
E. Represent expenses (other than labor). 
Then the market value of the rubber collected from one tree at 
a single tapping, less the cost of collecting same in laborers' time, 
multiplied by the total number of tappings per year on all the 
trees, less general expenses other than labor, will be the total profit 
for the year. Dividing this by the capital invested will give the 
percentage of profit on the investment or ; 
L 
Percentage of profit on capital invested— A x T (p ^" n) ~ F - 
In this equation the value of X varies directly as C and inversly 
as y. The more trees planted to the acre or the larger X is the 
smaller the yield y will be and also the larger the capital to be 
invested, C. Then again the more py exceeds ^ the greater will 
be the profit. Experience must determine what effect increasing 
N has upon the value of p and y ; hence to arrive at the number 
of trees per acre that it is best to plant in order to try and obtain 
a maximum value of the percentage of profit on the capital in- 
vested we must consider : 
C. Capital invested. 
L. Cost of labor when trees come into bearing and also what 
it will be in the next ten and twenty years. 
p. Market price of rubber in five, ten and more years, 
y. Yield per tree at each single tapping. 
