136 Transactions of the South African Philosophical Soctety. 
On looking through this table the one feature that is pre- 
eminently striking beyond all others is the difference in compo- 
sition between the alluvial soil No. 8, and all the rest, which are 
primary granite.soils. In the essentials of plant food it is far 
richer than any other soil. Excluding, then, that sample, we get 
the following as the average content of the remaining twenty 
primary granitic soils (I have added the maximum and minimum 
in respect of each constituent) :— 
LIME. POTASH. PHOSPHORIC OXIDE. 
Min. AV. Max. Min. Av. Max. Min. AV. ax. 
037 1°81 002 = -025 °056 trace "014 ‘075 
That is to say, the average primary granite soil is poor in all 
three of the above-mentioned constituents, but of course it will be 
remembered that many of these soils have been under lengthened 
cultivation. The poverty of the soil is due to the fact that the 
minerals of which the granite is composed have not been com- 
pletely disintegrated, and thus the plant food they contain, though 
present, is not present in aform available to the plant. For instance, 
in the case of soil No. 1, the felspar, from which the lime is derived, 
had remained undecomposed, and hence the sample contained no 
available lime. A comparison between samples 3 and 4 is interest- 
ing: though the former was richer in potash and phosphoric oxide, 
it was quite destitute of available lime; no wonder, therefore, that 
the vines on this patch were found to be sickly, whereas the quantity 
of lime in sample No. 4, small though it was, sufficed to maintain 
the vines in health. Compare also Nos. 5 and 6: on the latter soil 
the vines were in good condition, on the former they were diseased. 
A supply of lime was subsequently given to soil No. 5, and the 
disease disappeared at once. Between Nos. 11 and 12 a similar 
comparison holds good, with this in addition—that No. 11 is excep- 
tionally poor in both phosphates and lime. Leaving out of account 
the alluvial soil No. 8, there is not one amongst the series that could 
be described as having a normal percentage of lime for agricultural 
purposes: there is a fair amount in No. 15, but all the otners are 
decidedly poor in that constituent. Nos. 3 and 7 have a fair amount 
of potash, but here too all the others, excepting of course No. 8, are 
poor. Nos. 3 and 6 contain phosphoric oxide in fair amount, the rest 
are poor, some extremely so. 
I may mention that I have regarded as poor any soil containing 
less than ‘1 per cent. of lime, or :05 per cent. of potash or phosphoric 
oxide, the normal amounts being ‘25 to ‘5 per cent. for lime, ‘15 to -25 
per cent. for potash, and -1 per cent. for phosphoric oxide. 
