June, 1909.] 



531 



Edible Products, 



with mineral and other substances, such 

 minerals as possess the power of pene- 

 trating the membrane ooze through and 

 continue to do so until the liquid on the 

 internal side of the membrane is as 

 highly charged as that on the external 

 side. This action of soil water passing 

 into the root hairs is called osmosis, and 

 the same process goes on when the 

 planter of epicurean taste soaks his 

 prunes in gin. 



If the plant uses any of the materials 

 dissolved in the soil water, they are 

 constantly withdrawn from the inner 

 surface of the membrane aud employed 

 for the purposes of plant nutrition, a 

 fresh quantity entering to take the 

 place of that which has been utilised. 

 Thus the total amount of these useful 

 substances taken into the plant by the 

 root may be actually very great, despite 

 the insignificant quantity contained in 

 the external soil water. On the other 

 hand, the passage of any useless or 

 injurious substances into the plant is 

 limited in so far as such materials are 

 not steadily utilised as fast as they pass 

 through the membrane, and so the 

 internal liquid in contact with the 

 absorbing surface soon gets as highly 

 charged as the liquid without, aud 

 absorption is then at an end. Here I 

 should like to caution you that when 

 dealing with concentrated chemical 

 manures, particularly nitrate of soda, 

 great care should be taken not to apply 

 more than is recommended, or else the 

 plant will be forced to absorb more 

 nitrate than is necessary for its healthy 

 welfare. 



Analysis of Tea Soils. 



A complete chemical analysis of our 

 old tea soils would generally show that 

 there is a large surplus of plant food 

 present, aud yet, unless the soil be 

 enriched with additional manures, the 

 yield of our bushes falls off. Hall, in 

 his book on the soil, says ' that even the 

 poorest soil contains the nutrient 

 material required by an ordinary crop 

 many times over,' yet we know that 

 crops respond vigorously to dressings of 

 manure which only add a fraction to 

 the plant-food already stored in the 

 soil. Evidence of the enormous stores 

 of plant food in the soil and the com- 

 parative slowness with which they can be 

 utilised has been proved at Rothamsted 

 Experimental Station. 



We are driven to conclude that the 

 nitrogen, potash, and phosphoric acid 

 are present in the soil in some other 

 mode of combination than the form in 

 which they exist in manures • so that 

 although they may be in the soil, they 

 are in such a state as to be very partially 



of service to the growing plant. The 

 soil must, therefore, be regarded as 

 possessing most of its plant food in 

 states of combination that cannot be 

 utilised by the plant, and these forms 

 slowly pass, by weathering and other 

 changes, into material which is available 

 for the crop. 



Chemists have recently learnt to dis- 

 tinguish between the total plant food in 

 the soil, and the available or " present 

 consumption " supply. Fertility analyses 

 are now made by agricultural analysts 

 whereby the approximate amouut of 

 plant food soluble in the soil water and 

 in the acid sap of the root is determined. 

 Without accepting present methods as 

 beyond all question it is yet an undoubt- 

 ed fact that whereas the old time 

 " complete" analysis was more often 

 than not a misleading and mischievous 

 guide, the modern " fertility " analysis 

 has been found a sound and reliable 

 indication of the real requirements 

 of the soil. Chemical analysis is not 

 the only means of solving this pro- 

 blem, and perhaps the very best way 

 of deciding upon the actual needs of 

 the soil is that of experimenting with 

 bushes which have been treated with 

 nitrates, phosphates and potash alone 

 and combined. 



A large number of practical experi- 

 ments, as we all know, have recently 

 been carried out at the Heeleaka Experi- 

 mental Station, but, I believe, the soil 

 there is of a sandy nature and the 

 results from using the same manures on 

 our soils might be misleading. 



The Heeleaka Experiments, 

 The Heeleaka experiments have taught 

 us a great deal, but I should recommend 

 every planter to carry out a careful 

 series of experiments on the Heeleaka 

 plan on his own garden ; at any rate all 

 the experiments that have given good 

 results ought to be tried. 



The principal constituents taken by a 

 tea bush from the soil are nitrogen, 

 potash and phosphoric acid. A manure 

 to be of any value must, therefore, 

 contain one or moie of these substances ; 

 for the most fertile soils could not endure 

 for any length of time the constant loss of 

 these ingi^edients vithout, in time, be- 

 coming impoverished. The principles of 

 the application of manures are to return 

 to the scil those ingredients which have 

 been removed by cropping, to make up 

 deficiencies in soils which are naturally 

 poor, and to supply the necessary food 

 substances for the growth of the future 

 crop. We must not forget, however, 

 that manures not only add to the 

 fertility of the soil by supplying direct 

 plant-food, but that some of them have 



