NUTRITION : THE WORK AND THE MATERIALS. 13 



solutions to effect the changes he wishes to bring about, 

 and just as the gardener sows the spawn or germs of 

 mushrooms in his mushroom bed, and obtains thereby a 

 crop of succulent fungi, so the farmer may be able to apply 

 to the soil the ferment-producing germs needed to change 

 its quality, and render it available for plant food. When 

 we have arrived at that point, manuring will be reduced to 

 a science, and a pinch of the right material will be as 

 efficient as a ton of our present compounds, the larger part 

 of which are undoubtedly wasted under existing circum- 

 stances. 



Potash salts are also essential, more so in some cases 

 than in others. At Eothamsted, potash, after having been 

 employed for a number of years as a manure- constituent on 

 a certain grass plot, was discontinued ; the produce, in con- 

 sequence, rapidly declined, and the quantity of carbon fixed 

 in the tissues of the plants proportionately diminished, 

 although the amount of nitrogen absorbed was the same in 

 the two cases. The presence, therefore, of an adequate supply 

 of potash, in the soil, seems essential to the full assimilation 

 of the carbon which is derived, as we shall presently see, from 

 the air, in the form of carbonic acid gas. It is believed from 

 recent experiments that without potash no starch can be 

 formed ; and starch, as we shall see hereafter, is of primary 

 importance in the nutrition of the plant. In any case the 

 value of potash manures for increasing the yield of certain 

 crops, particularly potatoes, is a fact beyond dispute. 



Sulphur and phosphorus are also derived from the soil 

 as sulphates and phosphates. Both occur in association 

 with the albuminoid contents of the protoplasm ; and phos- 

 phorus seems specially needful in the formation of the 

 pollen the fertilising powder in the flowers and in the 



