116 
different high-yielders should be planted as far away as possible 
from other Heveas. The nursery would then consist of two 
physiological individuals, and natural cross-fertilisation should 
result. A plantation of grafted trees from more than two female 
parents is not to be reeommended—it becomes impossible to check 
the origin of the second generation, and the question of selection 
is unduly complicated. 
of descendants as good as, or 
parent. The best trees raised are then planted out in fresh 
nurseries. In each succeeding generation the quality of the seed 
ill improve 
_ A plan of the nursery is given by Dr. Heusser, showing the 
trees grafted from the two individuals in unequal numbers; so 
that should self-fertilisation occur, the fewer trees of one indivi- 
dual can be cut out without disadvantage. The plants are spaced 
m. : 
Artificial crossing of good-yielders may be carried out in the 
lantation, if an isolated nursery cannot be made, and there is the 
urther advantage that the first nursery generation would thus be 
avoided. In practice, however, it is laborious. In order to reach 
the flowers of the female parent the erection of light scaffolding is 
generally necessary. Before the opening of the female flowers, 
the inflorescences must be enclosed in a gauze balloon. The 
they are the product of one particular tree (see in this connection 
K. B.. 1919, p. 318). 
The main objection to selection by seed is the long waiting 
period before a highly productive strain can be established. 
Before a young Hevea reaches seed-bearing age some 3-5 years 
must elapse, and even then a tree cannot be relied on with any 
certainty. 
A second factor that may handicap the work of seed selection 
is the manner in which characters are inherited. It appears that 
high latex production is the result of several factors, and that if 
a2 
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