1 86 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



positions of plant residues going on in the soil are substantial^ the 

 same in all soils, but that the speed at which they take place varies, 

 and may be slower than the speed at which the residues accumulate. 

 These residues impart characteristic properties to the soils. It is thus 

 possible to classify soils on the basis of the speed of decomposition 

 as follows : — 



Decomposition of residues 

 quicker than accumulation. 



Decomposition of residues slower than rate of accumulation. 



Normal soils. 



Delayed by 

 dryness. 



Delayed by excessive wetness. 



Delayed by 

 cold. 



1 



Calcium carbo- Calcium carbo- 

 nate lackiDg. nate present. 



Sands 

 Loams 

 Clays 



Heaths 

 Steppes 



Peats Fen 



Moors ! Black soils 



I 



l 



Tundra 



This scheme has the advantage of bringing out the fundamental 

 law that the properties of a given soil are determined largely by its 

 history. The climate to which it has been exposed plays a controlling 

 part in determining the vegetation it carried in the past, while both 

 factors determine the vegetation it can carry to-day. 



One final reflection suggests itself. This cycle of change on which 

 depends the success of our crops and our gardens is the work of soil 

 organisms, but it is hardly likely to be the sole work of all the great 

 variety one finds there. Can we step in and control the process, 

 and make the organisms more useful ? The idea of sitting down 

 and directing things instead of labouring to do them has always 

 been one of the laudable ambitions of mankind, and efforts have not 

 been wanting to control the soil bacteria. 



The attempt began some twenty-five years ago, when it was found 

 that leguminous plants could be made to grow on the most sterile 

 sand, manured only with calcium carbonate, potash, and phosphates, 

 by the simple expedient of inoculating with the necessary bacteria. 

 Nothing is easier than to put bacteria into the soil, and it was thought 

 that if nothing else were needed then truly the golden age had come 

 to the husbandman. The desire to get something for nothing is 

 deeply implanted in the human breast, and here seemed to be ful- 

 filment complete beyond the wildest hopes of the most visionary 

 schemers. Unfortunately, inoculation has not come up to expectations : 

 before it can hope to succeed all the soil conditions have to be made 

 favourable both to the organisms and the plant ; drainage, cultivation, 

 supply of calcium carbonate, phosphates, potassium salts, moisture, 

 suitable temperature, depth of soil all have to be provided, and 

 by the time this is done the soil has generally been so greatly improved 

 that inoculation is unnecessary. A few successful cases are on record 

 where it may be presumed the necessary organisms were entirely 

 lacking from the soil, but they are the exception and not the rule. 



