only true medium for the conveyance of mineral salts to the plant.* The 

 variable root-action of different plants rendered all the more complex the 

 problem of discovering a solvent that would suit all cases. 



Ere long one of the fundamental principles of Toll's theory was ad- 

 mitted to due recognition. Obviously no plant food constituents in a soil 

 could be considered as "available" when present in compact impermeable 

 masses : hence became clear the advisability of agreement with regard to 

 ihe size of soil particles to be included in any determination. The result 

 was a consensus of opinion that 110 plant food substances in any soil could 

 be held to be available unless they were contained in soil particles not ex- 

 ceeding a definite maximum diameter. It therefore became customary, 

 when analysing a soil for agricultural purposes, to pass it through a sieve 

 of standard mesh before proceeding with the chemical analysis, disre- 

 garding for that purpose all that failed to pass through. f 



Scientific progress with regard to the chemistry of agricultural soila 

 had about reached this stage- when the circumstances occurred which led 

 to the writer's undertaking the systematic investigation of the soils of the 

 ape Colony. How this came about may be very briefly explained. 



In 1890 the writer was engaged, in connection with the Fellowship 

 granted him by the University of the Cape of Good Hope, in the analysis 

 of specimens of oathay from various parts of the Colony, and, in comment- 

 ing upon the results of his investigations, made use of the following words : 



" Another noteworthy fact, one which our farmers should bear in rnind, i.s this, that 

 the oathay from the Western Province contains an exceptionally small amount of lime, 

 this being due entirely to a deficiency of lime in the soil, a deficiency which it becomes 

 absolutely necessary to meet by the artificial application of lime manures to the soil. . . . 

 The sample of oathay from Port Alfred contained an exceedingly small quantity of 

 phosphoric oxide, and to this, doubtless, is due the poor appearance of the sample, its 

 weight being about one-fourth, or less, of what it should have been under normal 

 conditions. I have been informed that the Veterinary Surgeon holds the opinion that the 

 cattle diseases in this district are probably due to a deficiency of phosphates in the food, 

 and the results of these investigations appear to confirm that view ; in fact, judging from 

 the analyses of the plants only, I should say that the soil of the Colony generally appears 

 "to be rather poor in phosphates." 



In the case just quoted the oats had been found to contain so little 

 phosphoric oxide as to cause wonder that such dwarfed and sickly-looking 

 plants had reached maturity at all, and the natural conclusion at the time 

 was that the soil upon which the cereal crop was grown was likewise de- 

 ficient in phosphates, and that, consequently, the opinion, said to have 

 been expressed by the Government Veterinary Surgeon, was, at any rate, 

 likely to be correct. In addressing a public meeting shortly afterwards, 

 the writer took occasion again to refer to the subject, and then observed : 

 " I do not regard the matter as settled satisfactorily, and commend it to 

 the attention of the Grahamstown Agricultural School, hoping that ere 

 long proper investigations will be made and the mystery cleared up." 



* " It seems entirely unnecessary, in studying the question of the nutrition and yield 

 of crops, to introduce artificial digestion media known to attack minerals very slightly 

 soluble in water, while it seems perfectly logical to accept the nutrient solution as it 

 exists in the soil as the basis for the support of plant life, and to investigate the question 

 along this line. In other words, it has seemed best to consider the soil as a culture medium 

 containing a nutrient solution that is, to regard the soil moisture as a proper and sufficient 

 medium for the feeding of plants, and the soil as a reservoir and distributing agent for this 

 solution." (M. Whitney & F. K. Cameron : " The chemistry of the soil as related to crop 

 production." 1903, p. 15). 



"The delivery of water from the soil to the plant must receive more consideration in 

 iuture chemical studies of soils for the reason that it is the mechanism by which the 

 mineral nutrients are supplied to the plant, and it is evident that if the delivery be email 

 ihe plant will suffer not only for water itself, but also for the mineral food which the 

 water supplies, even though ample quantities may be present in the soil solution, and in 

 Tvhat would usually be regarded as readily available form " (7fo'<?., p. 6P .) 



t But see also page 13. 



