jor January, 1920 



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I A Lesson on Soil Formation and Its Bacteria I 



Being One of a Series ot Lessons of a Home Study Course on (hardening. Appearing 



Under the Direction of ARTHUR SMITH 



Regularly in The Gardeners' Chronicle 



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IN choosing subjects to be dealt with in this department, 

 our aim has been to select those having some special 



connection with the work of the particular month in 

 which each appears. However, as at this time there is 

 little connected with gardening outside which can be 

 called seasonable, it appears that this is a fitting period 

 to spend a little while at the Fireside University and to 

 go somewhat deeper mto the whys and wherefores of 

 matters which have previously been given merely a 

 passing glance. 



We believe that gardeners, whether professional or 

 amateur — and we are glad to know that there are a con- 

 tinually increasing number of the latter who read this 

 journal — will always find that the more they know of the 

 complex processes which are going on in the soil and in 

 the plant, and the more they know of i^-liy certain re- 

 quirements are necessary to produce the highest results, 

 the more interesting the work will be and the more pleas- 

 ure they will derive in carrying it out. 



Subjects connected with the soil and plant life are so 

 co-related and so inextricably interwoven that it is a 

 practical impossibility to avoid at all i;imes some repeti- 

 tion in dealing with the various seasonable phases to 

 which they refer. 



SUIL POPULATION, BOTH GOOD AND EVIL. 



The soil, and the spectacle of a living plant growing 

 and building itself up from it, was the theme of some in- 

 teresting stories, both in prose and ver.se, written by the 

 most learned philosophers who lived several hundred 

 years before the Christian era, and from their writings 

 we gather that our practice today is. broadly speaking, 

 verv little, and in some ways not at all, farther advanced 

 than it was then. But we today know something about the 

 whvs and wherefores of which in those ancient times 

 nothing was known. About the first discovery relating to 

 causes was made at the beginning of the nineteenth cen- 

 tury by the application of analytical chemistry to both the 

 soil and the plant, but the most momentous and far- 

 reaching step along these lines was made only some 

 twenty-five years ago when the first knowledge of the 

 work of bacteria in connection with plant growth was 

 gained. Tliis discovery opened up a vast unexplored re- 

 gion, the boundaries of which have nut been reached, nor 

 are they in sight. 



Today we know that soils are peopled by myriads of 

 micro-organisms containing numerous distinct species, 

 each species carrying on its appointed work, which causes 

 the soil to be more suitable, or less suitable, according to 

 the nature of the work, for plant life. It has been esti- 

 mated that in a grain of average .soil there are from 

 sixty thousand to five hundred thousand beneficial and 

 injurious bacteria. (In case any reader should not be 

 aware of the fact, it may be mentioned that a gram 

 equals 15.432 grains avoirdupois.) 



This tremendous soil population is always busy, .\mong 

 them division of labor is the rule, and it has been foun<l 

 that certain species of bacteria are specialists along cer- 

 tain lines and along these only ; they carry out their 

 special work which may be changing organic matter 

 which is in a condition that is unavailable for the plant, 

 into one which is available. One species specializes in 

 making the initial change, when the work is taken up 



by another species which carries it along a step farther; 

 then a third takes it in hand, and so on, until the stage 

 is reached when the result of the process is perhaps an 

 ingredient that the plant will find suitable for its consump- 

 tion ; or the result may be something inimical to plant 

 life, either in the way of active poison to it, or poisonous 

 and directly destructive to those beneficial bacteria upon 

 which the plant demands more or less for its existence; 

 and in either case it is generally, but not always, a sub- 

 stance which cannot be carried to any other stage. 



It will be apparent therefore that the population of the 

 soil is composed of both good and evil, working along 

 lines similar to those followed by the human population 

 of the earth's surface. Among the latter a number are 

 working in various ways directly or indirectly connected 

 with productive industry; while others are at the same 

 time busy creating poisonous influences along the lines 

 of destruction to industry and destruction to the beneficial 

 workers. \'arious points in the more advanced practice 

 of gardeners and farmers (which will be touched upon 

 later on) are being increasingly devoted to preventing the 

 work of the harmful soil population both by bringing 

 about their actual destruction, as well as by using means 

 to foster, strengthen, and encourage the growth and mul- 

 tiplication of those members of the soil population which 

 are beneficial. 



THE M.\TEUIALS THAT COMPOSE THE SOIL. 



Before dealing somewhat more fully with the work of 

 these bacteria and showing why certain operations in gar- 

 dening are based upon the idea of creating conditions 

 suitable for those which work for the good of the plant, 

 it appears fitting that we should first consider very briefly 

 some points connected with the making of soil, a word 

 which was italicised above for the purpose of emphasiz- 

 ing the fact that material composing the earth's surface 

 cannot always be designated soil. 



The beginning of soil formation goes back to remote 

 ages when the particles of sand, grit or clay got split or 

 ground off the rocks and began their wanderings by 

 water, wind, or glacier that have finally deposited them 

 in their present place. Many of their chemical and me- 

 chanical properties were determined by the original rock 

 and also during these wanderings by mixture with debris 

 from other rocks, thereby creating differences which have 

 persisted through many ages, and wc cannot go back 

 and undo the work of the past. But the mineral particles 

 do not constitute the soil, although they average ninety- 

 five per cent of it. The final stage in soil formation is not 

 com[)lete until vegetation has sprung up and died, and 

 its remains have mingled with the mineral fragments and 

 decayed. During its lifetime vegetation takes certain sub- 

 stances from the mineral or inorganic matter and the 

 atmosphere, and builds them up into complex organic 

 nialter. Like other constructive work, this process re- 

 quires energy, which in this case is derived from the sun- 

 light and is stored up in the complex substances of the 

 cell tissues of the plants. 



When the plant dies and its remains mingle with the 

 mineral fragments, it begins to decay. The whole process 

 then reverses : instead of a building up there is a break- 

 ing down ; the fabric of complex material slowly elabo- 

 rated during life, is disintegrated and resolved into 



