( 5 ) 
of the tree. The magnitude of the variation in dry 
rubber production is thus very apparent, and it is 
clear that if pure races of these heavy yielding trees 
can be produced, then acreage productions on our 
estates will be vastly increased. The crux of the 
situation lies in the problem of isolating and pro- 
pagating pure races of these heavy yielding trees. 
This problem must be considered as distinct from 
that of the breeding of trees resistant to diseases 
or possessing other distinct characteristics. 
Two courses are available to the experimentalist: — 
Seed selection. 
Vegetative propagation. 
Seed selection. 
(i) Mass selection. 
(ii) Pedigree selection. 
It has been found that large heavy seeds of Hevea 
germinate more rapidly and produce stronger seed- 
lings than those derived from small and light seed, 
because they carry more food for the young plants 
and give them a better start in life. Therefore a 
rough grading of seed into light and heavy groups, 
with consequent use of the latter only, w r ill produce 
healthier nurseries than can be obtained from un- 
sorted seed, and thus ensure healthy stock for 
planting. This method is very superficial and does 
not take into account the inherent quality of each 
seed; nevertheless, in mixed populations, it is likely 
to have a good effect and is one of the few practices 
which every planter can adopt. Present methods of 
thinning out trees by selection based on the health 
and yields of individual trees is really a form of 
mass selection, though its effects can only be seen 
in the progeny derived from seed obtained from 
(M.'W'f 
