544 



The Weekly Florists^ Review* 



AtRlL 21, 189*. 



IV. The Bacteria of Reot Tuberclts. 



But there is another group of bac- 

 teria of exceeding grt-at importance to 

 which we now wish to turn our atten- 

 tion, i. e., the bacteria of the so-called 

 root-tubercles. 



In discussing the process induced by 

 the bacteria of putrefaction I have 

 said already that certain gases are 

 formed which pass off into the air. As 

 we well know the one of these gases 

 which is in greatest abundance is car- 

 bonic acid gas, one which may be 

 taken directly into the green leaves 

 and worked immediately into starch 

 and sugars. 



But among other things which are 

 set free by the bacteria in their work 

 of decomposition is a considerable 

 quantity of free nitrogen which passes 

 out into the atmosphere, and which 

 the leave's of plants have no power of 

 again taking up. If all plants were to 

 grow and die and decay in one place, 

 and should all the substances they 

 take from the soil be thus returned to 

 it by means of decomposition the soil 

 would never become impoverished but 

 would remain fertile. But as we And 

 that with every decomposition some 

 free nitrogen is lost, and since we 

 know that a great many plants or 

 parts of plants are constantly carried 

 away from the soil which produced 

 theni, so that they have no opportuni- 

 ty of enriching it by returning to it, it 

 becomes evident that this great loss of 

 nitrogen must be supplied in some 

 other way if we are going to maintain 

 the fertility of the soil. And here I 

 must refer again to our fertilizers. 

 Every successful horticulturist knows 

 that that fertilizer is best which con- 

 tains much available nitrogen com- 

 pounds. He has learned through prac- 

 tice to select those fertilizers which 

 can give to his soil the best recom- 

 pense for the nitrogen carried off into 

 the atmosphere and for the nitrogen 

 and other compounds which are lost 

 by removal from a soil of the plants 

 or animals which grew upon it. There 

 are many of these fertilizers — some 

 good — any many worse than worth- 

 less, but it is not a part of our present 

 plan to discuss their merits. In this 

 paper it is our purpose to deal with 

 nature's means of replenishing the 

 soil, rather than with artificial means. 



A great many years ago agricultur- 

 ists who raised corn and wheat found 

 that were these crops grown in one 

 place one after the other for many 

 years, the soil became so poor it would 

 no longer raise- a good crop of either. 

 And since soil so used would no longer 

 produce the plants most desired by 

 the farmer, he sowed a crop of clover 

 in order as he said "to let the soil 

 rest." And after having grown clover 

 one or two seasons he found his soil 

 again able to produce wheat or corn. 

 And for a long time such was the ex- 

 tent of our knowledge of the process. 

 Even when some one discovered on 

 the roots of clovers the small globules 

 now known as tubercles, they were, 

 called root-seeds, though it was well 



known that the se-eds which reproduce 

 the plants grow in ordinary flowers,^ 

 but later experiments showed that 

 other members of the family legumin- 

 osae — e. g. peas, beans, vetches, etc., 

 developed the same kind of tubercles 

 and could enrich the soil as well as 

 the clovers. Microscopical examina- 

 tion of the tubercles showed them to 

 be filled with bacteria, and the ob- 

 servers soon associated the presence 

 of the bacteria with the luxuriance of 

 the plants upon which they gre-w. It 

 was suggested that these bacteria were- 

 able to take from the atmosphere the 

 free nitrogen which the soil lacks, and 

 to work it into some form in which it 

 could be used as food by the higher 

 plants. Many papers have been writ- 

 ten and many recent experiments 

 made in attempts both to prove and 

 disprove this claim. It has been prov- 

 en conclusively that this suggestion 

 with reference to the function of these 

 tubercle bacteria is correct. The free 

 nitrogen of the atmosphere which can- 

 not be used by green plants can be 

 fixed by these small organisms. Some 

 of the nitrogen compounds thus form- 

 ed are used directly by the plant upon 

 which the tubercle grows. Some of it 

 not so used is left in the soil by the 

 final decay of the tubercle and may be 

 used by succeeding crops to be grown 

 in the same soil. 



That these things are true has been 

 proven by growing clovers, peas and 

 beans in soil in which all the bacteria 

 have been killed. In such cases no tu- 

 bercles were formed and the plants 

 grew very poorly. But when the tu- 

 bercle bacteria were introduced into 

 the same soil, tubercles were soon pro- 

 duced and the growth of the plants be- 

 came luxuriant. Examination of the 

 soil showed it to contain much more 

 of the compounds of nitrogen than be- 

 fore. 



Another clever experiment was made 

 to show that tubercles are never form- 

 ed in the absence of the tubercle bac- 

 teria. A plant was placed in a small 

 pot and some of the roots drawn 

 through an opening in the bottom. The 

 smaller pot was placed in a large one. 

 In one pot there was placed sterilized 

 soil and in the other ordinary garden 

 soil. The roots which were in the gar- 

 den soil produced tubercles and those 

 in the sterile soil produced none. 

 Many such experiments have been 

 made to show the same thing. 



There can be no longer any reason- 

 able doubt that the tubercle bacteria 

 are of the greatest importance in re- 

 claiming worn out soils by bringing 

 in from the atmosphere the nitrogen, 

 the absence of which constitutes the 

 poverty of the soil. So far this action 

 has been found to take place with 

 plants in the family leguminosae only. 

 Since scientific knowledge of this pro- 

 cess has been obtained members of 

 this family have been extensively 

 grown in order that the beneficial ef- 

 fects may be had. Several companies 

 have been formed which propose to 

 sell the tubercle bacteria, thus insur- 

 ing the purchaser in having the cor- 



rect forms with which his clovers, etc., 



may be grown. Such seems hardly 

 necessary since these tubercle germs 

 seem always to be present in the soil 

 and even to be able in some cases to 

 fix nitrogen in the absence of plant 

 roots. A few experiments have been 

 made with these commercial prepara- 

 tions of tubercle bacteria, but none so 

 far as now known have been reported 

 favorably, except by the persons desir- 

 ing to sell the preparations. It may 

 be that sometime a in-eparation will 

 be sold which will be better than the 

 bacteria supplied in the soil by nature, 

 but recent experiments do not point 

 in that direction. 



I think I may safely repeat that the 

 importance of the action of the bacte- 

 ria in the nutrition of plants can hard- 

 ly be overestimated. The bacteria of 

 putrefaction, by living in the dead 

 bodies of animals and plants, break 

 down the complex substances into 

 simple ones, some of which may be 

 again used directly by plants, others 

 of these decomposition products are 

 far too simple to be used directly and 

 are changed by the nitrifying bacteria 

 into nitrates which can be used as 

 plant food. Another decomposition 

 product — nitrogen — often escapes from 

 the decaying body into the atmosphere 

 and is brought back and again ren- 

 dered usable by the bacteria of the 

 root tubercles. The bacteria consti- 

 tute most important links in the food 

 cycle of plants and animals, and were 

 they absent most if not all the life of 

 the earth would soon be impossible. 

 Doubtless most of the elements of 

 food have been through the food cycle 

 times innumerable, built into complex 

 food substances through the direct or 

 indirect infiuence of the sun's rays, 

 and freed again from this complex 

 food and reduced to a usable form 

 through the action of the bacteria. 

 Through centuries of time the food 

 elements through the influence of the 

 sun, have been made into plant food. 

 From plants the food has been made 

 more complex in being built up into 

 animal bodies. After serving in the 

 animal body, the compounds are re- 

 duced by the bacteria to simple sub- 

 stances with which we began and the 

 substances with which we begin again 

 the never ending story which is ever 

 the same. 



GEORGE SAVAGE. 



It is with sincere regret and a feel- 

 ing of personal loss that the death of 

 George Savage is noted in the current 

 issues of the trade papers, and a word 

 or two from one who knew him from 

 the time he first came to this country 

 may not be out of place just now. 

 George Savage was a born plantsman 

 and a close observer, and during the 

 five years in which the writer acted as 

 assistant to Mr. Savage in the propa- 

 gating house of George Such's estab- 

 lishment, many were the interesting 

 discussions relative to the merits and 

 mode of treatment of various plants, 

 and the points thus gained have since 

 proved most valuable. 



