276 
“ Potash, one of the chief mineral constituents required for 
plant growth, is frequently deficient, though a few. of the river 
deposits are rich in this constituent, and the subsoil is usually 
richer than the surface soil especially if of a clayey nature. 
“ The proportion of phosphoric acid is also variable, ranging 
from 0.012 to 0.13, the average being about 0.76 per cent, on the 
air-dried soil. 
« All this class of soil requires very efficient drainage as it 
has Often been more or less under water for years, so that air 
has been excluded, resulting in a rather high proportion ot the 
lower oxide of iron, which in excess is poisonous to many culti- 
vated plants. The vigorous growth of rubber on this class ol 
soil after drainage is unequalled elsewhere during the first years 
of growth. 
“ Upland Soils.— These soils have a larger proportion of 
sand and coarser particles in their composition which renders 
them more open, and drainage, except for saving wash, less 
necessary. 
“ They are richer in nitrogen than the proportion of organic 
matter would indicate, but are usually a little deficient in total 
potash and to some extent in phosphoric acid. 
“ Their free character and suitability for root growth makes 
the proportion of these constituents ample for present require- 
ments, and it is evident from the growth of Para on these sous 
that there is no deficiency in any respect. 
