19, 4 Reinking and Groff: Siamese Seedless Pummelo 413 
fluence this condition, and the application of paddy ash is said 
greatly to reduce the danger of its occurrence. 
Paddy ash consists of the ash of burned rice husks, of which 
a plentiful supply is always obtainable in the vicinity of Bangkok. 
Many large rice mills operate within this region, and the husks 
of the grain are used as fuel. At the rice mills this paddy ash 
is often dumped, because it cannot be sold or even removed 
for fertilizer. It is naturally a valuable source of potash and 
is recognized by all successful pummelo growers as an import- 
ant fertilizing element. It is usually applied to the surface of 
the beds, small piles being placed under the trees and allowed 
to work to the roots gradually. These piles can be found at the 
base of many pummelo trees in Nakorn Chaisri (Plate 9, fig. 3). 
_ In addition to the above sources of fertilizer, night soil is some- 
times used. Small holes are dug in the beds under the limbs 
of the tree, and .the night soil is poured in and allowed to find 
its way to the roots. Apparently this practice is not followed 
to the same extent that it is in China. 
PRUNING 
Growers pay little attention to systematic pruning, except to 
cut out all dead branches. Shapely, low-headed trees are con- 
sidered just as important in Nakorn Chaisri (Plate 10, fig. 1) 
as they are in any western citrus grove. Trees of this shape 
are obtained not by pruning, but by the careful selection of suit- 
able branches of layering. These are so planted as to have 
the forked head only a few centimeters above the ground. The 
lower branches of the trees are then encouraged to lie almost flat 
along the surface of the bed, in many cases finally extending over 
the trench of water (Plate 10, fig. 2). In old pummelo groves 
very severe cutting back of trees is practiced. The question of 
the proper amount of pruning under tropical conditions is 
another interesting experimental field. Doubtless growers are 
erring on the safe side in not pruning too severely trees that 
have practically no period of rest. 
PROPAGATION 
Western methods of propagating citrus have never been in- 
troduced into Siam, and the methods followed are almost en- 
tirely those used by the southern Chinese in their fruit culture. 
. In Nakorn Chaisri the pummelos are multiplied by marcottage, 
or Chinese air layering. In this way desirable parent plants 
are used for propagation and good strains of the variety are 
