138 University of California Publications in Agricultural Sciences [Vol. 1 



cases, though not so marked, have been commented on elsewhere 

 by one of us (see literature above cited). While the sulfates 

 of all the metals named are toxic to ammonification, and in very 

 low as well as very high concentrations, ranging from 50 parts 

 per million to 2500 parts per million, they manifest a relatively 

 low toxicity for the flora concerned in that phase of nitrogen 

 transformation. On the other hand, all the same metals exercise, 

 in a large variety of concentrations, a marked stimulating effect 

 on the nitrifying flora. That differences of such magnitude 

 should exist between two flora of the soil, one being presumably 

 dependent for its raw material on the other, is, to say the least, 

 amazing and not wholly explicable. Since, however, nitrification 

 in the broader sense of the term represents the algebraic sum of 

 the activities of all forms of nitrogen-transforming bacteria in 

 the soil, it would appear from our results that the net effect of 

 the activity of the metallic salts tested is to insure a larger 

 nitrate supply in the soil. This must be so, since in the most 

 extreme cases above studied ammonification is depressed only 

 to an extent which lowers the total ammonia yields below that 

 of the salt-free soil by about 30 per cent, whereas nitrate pro- 

 duction is frequently enhanced in efficiency by the presence of 

 the same metals to an extent which doubles the yield of a normal 

 soil flora. 



Our findings would therefore render much easier the explana- 

 tion of the oft-noted stimulating effect of copper, in particular, 

 and metallic salts in general (in proper concentrations), on the 

 higher plants, regarding which, also, we have accumulated con- 

 siderable data. If a larger nitrate production in the soil follows 

 the application of a metallic salt as above shown, the nitrogen 

 nutrition of plants must go on with greater facility and adequacy ; 

 hence increased growth. 



As above intimated, the underlying causes of our very inter- 

 esting results are not easy to discover. In addition, however, to 

 the speculations on that subject which we make, and which we 

 recognize for more reasons than one as far from satisfying, we 

 have obtained some experimental evidence on the point in ques- 

 tion which possesses more cogency. It appears from these that 

 water absorption is hastened by germinating seeds and young 



