July 1], 1913] 



SCIENCE 



49 



interested in finding out what limits the ac- 

 tivity of the bacteria in the soil, then they and 

 I are working upon two different problems. It 

 would appear, however, that they wish to find 

 out what it is that limits the bacterial activity 

 in order that they can say that when this bac- 

 terial activity is limited there is a lessened 

 ammonification, so that they may make the 

 further assumption that when there is lessened 

 ammonification there is of necessity a lessened 

 yield of grain on the soil. In other words, 

 they would account for the lessened or deterio- 

 rated grain product on such soils. In their 

 regular reports in the Journal of Agricultural 

 Science, they have actually made such thought 

 transfers. 



We have gone at the problem more directly in 

 our experiments with the purpose in view of as- 

 certaining what it is that tends to limit the 

 grain production or to bring about deteriorated 

 grain on fertile soils, and in doing so we have 

 found that if we bring about rather perfect 

 sterilization in potted soils, the limiting factor 

 on grain production is done away with, pro- 

 vided we do not reintroduce it by means of 

 internally infected seeds or other wheat dis- 

 ease-producing matters. Bacteria and amoebaB 

 do not seem to play any primary part in this 

 problem of deteriorated cereal crops. 



The chemists have so thoroughly filled our 

 minds with their belief that improvement in 

 grain production or deterioration in grain 

 production can only he accounted for because 

 of modified elements of plant food that it would 

 seem that some bacteriologists are coloring 

 much of their work with an attempt to prove 

 that bacteria are necessary to bring about those 

 modifications which the chemists assume to 

 take place. 



The peculiar thing which our experiments 

 make plain is that when we have a purified 

 seedling placed in a purified soil, they show 

 no element of weakness or tendency to deterio- 

 rate. Furthermore, our experiments do not 

 show any particular necessary relationship as- 

 sociated with ammonification and such plant 

 production. Deterioration takes place regard- 

 less of the presence or absence of high ammoni- 

 fication. We find, in ordinary soils, that a 



rather poor soil can produce perfect wheat 

 seeds if free from parasitic organisms. We 

 find also that a rich soil can not produce per- 

 fect wheat, regardless of its fertility and the 

 amount of ammonification, if certain organ- 

 isms are present in the soil or the seed. 



Finally, I agree with Messrs. Eussell and 

 Hutchinson that microorganic population of 

 the soil is " very complex," and would call 

 their attention to the fact that in order to 

 produce wheat on certain kinds of soil they 

 will have to find types of amceba or other 

 microorganism which will be capable of eating 

 some very large fungi endways. Though we 

 have checked up much of the work on soil 

 toxines and gone into the bacterial proposi- 

 tion very carefully, especially with regard to 

 ammonification, I yet must say that I am un- 

 able to find any cereal crop-limiting factors of 

 any importance associated either with indefi- 

 nite toxic substances or with the activity of 

 bacteria. Having a given amount of available 

 fertility, the plants get along. We have, how- 

 ever, found that there are at least one or more 

 species each of the following mold-like fungi 

 which, when in the soil, are real cereal crop- 

 limiting factors: Fusarium, AUernaria, Hel- 

 minthosporium, Colletotrichum, Macrosporium 

 and Ophioholus. 



We find that most of these organisms are 

 not only persistent in the soil, remaining there 

 by way of the stubble and roots of their host 

 plants, but may be introduced with the seed, 

 fresh or improperly composted manures, etc., 

 most of them being what may be spoken of as 

 internal seed-infecting organisms. I would 

 again call attention to what to me is an evi- 

 dent fact: that those who are working on the 

 bacterial and toxine phases of the question of 

 soil fertility will never have any results which 

 they are justified in making use of until they 

 are able to plant disease-free seedlings either 

 in the soil or in their special cultures and to 

 eliminate the disease factor in the soil. We 

 have, of course, conducted many experiments, 

 or I would not feel justified in making so 

 strong statements as these. Were the problem 

 of the soil fungi in wheat chopping less com- 

 plex, I should long since have been giving out 



