240 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
workable after heavy liming, and it was found there by careful estima- 
tions that the application of 200 lb. of ammonium salts caused the 
removal of 120 lb. of calcium carbonate. 
Lime has a further and more complicated chemical action which is 
indicated by the chart on page 236. From this it will be seen that 
lime plays an important part in rendering the three chief ingredients 
of the soil (nitrogen, potash, and phosphates) available for plant 
nutrition and retaining them in this form. Nitrogen, as is well 
known, is chiefly obtained by the plant in the form of nitrates, which are 
produced from humus and ammonia by a process of decay carried on 
by a group of micro-organisms known as the nitrifying bacteria. The 
first product of this decay is ammonium carbonate. The ammonia is 
then attacked by another group of bacteria, and nitrites are formed, 
this process requiring the presence of lime. A third group of bacteria 
then attacks the nitrites and converts them into nitrates, which ally 
themselves with lime, forming calcium nitrate, a soluble neutral salt 
that can be taken up by the plant. It will be seen later that none of 
these beneficent bacteria can work in an acid medium. The action 
of lime on the potash in the soil is purely chemical. This important 
plant-food is present in all soils, especially those of a clayey nature 
but in a very insoluble form, generally as a complex compound of 
potash and alumina ; when lime comes in contact with such a com- 
pound, being an active base, it will take the place of potash, which, 
being thus liberated, goes into solution and becomes available for the 
plant. By the activity that lime possesses as a base it also assists in 
retaining in the soil in an available form the potash added in manures. 
The chemical action of lime on the phosphoric acid in the soil is perhaps 
equally important. The store of phosphates in the soil is largely 
composed of phosphates of alumina and iron ; on these lime acts in the 
same way, namely as an active base, taking the place of the alumina 
and iron and forming phosphates of calcium, which easily become 
available as plant -food. Again, the phosphates added in manures, 
especially those applied in an acid form, such as superphosphate, are 
retained in the soil as calcium diphosphate, which easily becomes 
soluble. 
Biological Action of Lime on the Soil. — Recent investigation has 
shown that the soil is not merely a storehouse for the food materials 
necessary to the plant, but that it is a factory peopled by millions of 
minute organisms on whose activities we depend for the conversion of 
the food materials present in the soil, or added in the form of manures, 
into the soluble state in which the delicate root hairs of the plant can 
absorb them. It is impossible in the scope of this paper to deal with 
this fascinating subject. We have already seen the important function 
played by the nitrifying bacteria in rendering available the ammonia 
present in the soil. Besides the nitrifying bacteria, there are many 
other beneficial bacteria whose work is of the utmost importance to 
the fertility of the soil. Two of the best -known instances are the 
Azotobacter, which has the power of fixing in the soil the free nitrogen 
