August 22, 1913] 



SCIENCE 



257 



mal weather conditions do not always 

 measure the crop in yield and seldom in 

 quality. He settles the matter by citing 

 the probability of soil depletion in some 

 measurable available matter of plant food; 

 when this is supplied, if the crop yet fails, 

 he eircumlocutes the question by the asser- 

 tion that there is "bad agriculture," and 

 if the farmer is unconvinced, he and the 

 farmer together are apt to blame the 

 weather or the variety. 



2. The Toxine Theory : The farmer, used 

 to the observation that a single crop system 

 sometimes gives sickly-looking plants and 

 failing crops, and that a long rest of the 

 land or a change of crop seems to tend to 

 correct the difficulty, and associating these 

 conditions with the well-known fact that 

 animals, including man, too closely housed 

 and associated with their own kind in large 

 numbers fail to thrive, has always had a 

 dim suspicion that when certain cropping 

 plants are too thick on the land or too con- 

 tinuously returned there, they may tend to 

 poison the ground for their own growth. 

 Certain bacteriologieally inclined chemists, 

 or rather, perhaps, bacteriologists with 

 chemical training, unduly impressed with 

 the fact that animals and plants and espe- 

 cially bacteria in a closed space throw off 

 substances toxic to themselves, have of late 

 invented a very plausible poison, toxine or 

 excreta theory by which they reason that 

 plants may poison themselves or introduce 

 into the soil substances poisonous to follow- 

 ing crops of the same sort. Some even go 

 so far, apparently, as to believe that almost 

 any soil may contain such organic sub- 

 stances. Thus, for example, Russell and 

 Hutchinson, of Eothamsted, seem to think 

 that a study of cabbage-sick soil might ex- 

 plain barley-sickness; that a study of sew- 

 age-logged soil might explain wheat-sick- 

 ness on arable soils, and Professor Whitney 

 has even tried to explain that grass fails to 



grow under a tree because of the excreta 

 thrown off by the tree. 



3. The Ammonification Theory: Certain 

 of the bacteriologists, over-enthusiastic as 

 to the efficacious power of bacteria to 

 change organic substances into nitrate ni- 

 trogen, etc., seem to imagine that culti- 

 vated plants could not live in fertile soil 

 without the activity of such organisms. 

 Unable to get away from their chemical 

 training, they attribute almost all of the 

 powers of a soil to produce a crop to the 

 bacterial flora, and have builded about bac- 

 terial activities what I think I am correct 

 in naming the "nitrification, ammonifica- 

 tion denitrification theory" of crop pro- 

 duction, until, when one reads their wri- 

 tings he must, if he assents to their as- 

 sumptions, believe that a wheat plant could 

 not be expected to thrive in a fertile soil in 

 the absence of such nitrifiers, ammonifiers 

 and denitrifiers in fine adjustment. 



4. The Amoeboid or Denitrification The- 

 ory: Finally, at Rothamsted, England, a 

 subdivision of the latter school of chemical 

 bacteriologists has risen who would grant 

 the essentials of the ammonification theory, 

 but are unable to account for the fact that 

 often in the presence of a highly nitro- 

 genous and otherwise fertile soil there is 

 yet crop failure and irregularity of crop 

 as to quality. They would explain such 

 irregularities or apparent soil deficiencies 

 in crop production by assuming that the 

 proper balance of bacterial flora in the soil 

 has been interfered with. This they ex- 

 plain by the assumption (wholly ground- 

 less, I think) that certain amoebee or other 

 organisms, which, for lack of better name, 

 they call biological factors, eat up the good 

 bacteria, the nitrifiers and ammonifiers and 

 for some reason are unable to digest the 

 denitrifiers, forgetting, apparently, the 

 short life of all of the organisms thus con- 

 cerned and the evident fact that such a 



