584 



SCIENCE 



[N. S. Vol. XXXVI. No. 931 



the amido and imido groups of the protein 

 molecules, a reduction must take place. 



It is obvious that the plant must spend 

 considerable energy in making this trans- 

 formation. What is more reasonable than 

 to suppose that the unit parts of the com- 

 plex protein molecules, when presented to 

 the plant, will be vised by it in preference 

 to expending labor on the nitrate to pre- 

 pare these units? If a soil be liberally 

 supplied with all of these units, it is con- 

 ceivable that good plant growth will result, 

 even without nitrate. If only a limited 

 amount or kind of the units be present, the 

 plant must have nitrates with which to 

 supply the missing units. The knowledge, 

 therefore, that such compounds exist in 

 soils and play such a prominent part in 

 the metabolism of the growing plant is of 

 fundamental significance in soil fertility 

 and gives a breadth of view to the subject 

 which in its horizon can not be compared 

 with the restricted vision imposed by the 

 purely mineral requirement theory of 

 Liebig, as this is used by his followers. 



Nitrates are not produced in these cul- 

 tures. Ammonia if formed is insignificant 

 in amount, nor does ammonia produce the 

 striking results shown by these organic 

 compounds. There is a limit to the 

 amount of any one of these soil constitu- 

 ents which the plant can profitably use and 

 show increased growth. When a mixture 

 of several of these units is presented at 

 once, the growth is better than if an 

 equivalent or even larger amount of any 

 single one is presented. 



These compounds are nitrogenous, but it 

 must not be inferred that all nitrogenous 

 compounds are beneficial to plant growth. 

 Tyrosine, also a degradation product of 

 protein, is distinctly harmful, and picoline 

 carboxylic acid, isolated from soils, is mod- 

 erately toxic. Guanidine, a compound not 

 yet isolated from soils but whose presence 



is indicated, has also been rather thor- 

 oughly studied, and is decidedly harmful to 

 plants, producing an effect on the cultures 

 similar to that shown by certain plant dis- 

 eases. The leaves become spotted with 

 bleached dots, which spread and ultimately 

 coalesce, producing a wilting of the plant 

 and finally death. Not only is the guan- 

 idine harmful, in contradistinction to the 

 beneficial nitrogenous substances just dis- 

 cussed, but it also differs from these com- 

 pounds in its behavior when nitrates are 

 present. The latter fertilizer ingredient 

 very greatly increases the toxic action of 

 this compound. This is especially stri- 

 king when a large series of cultures with 

 and without guanidine in the presence of 

 many ratios of phosphate, potash and 

 nitrate is set up and the cultures arranged 

 according to the nitrate content. Both 

 groups of cultures with and without guan- 

 idine will grow nicely for three or four 

 days without any peculiarity being notice- 

 able in either group. The cultures high 

 in nitrates will be the first to show the 

 symptoms of guanidine poisoning, and this 

 effect will spread through the guanidine 

 group of cultures, becoming more and more 

 marked in those high in nitrates. At the 

 conclusion of two weeks the group of cul- 

 tures containing no guanidine will appear 

 green and fresh, whereas the guanidine 

 group appears bleached and wilted in all 

 of the cultures containing nitrates. The 

 cultures which contain no nitrate, that is, 

 only potash and phosphate, are the only 

 cultures which have been able to withstand 

 the ravages of this poisonous compound. 

 We have here a striking illustration not 

 only of the harmful effect of an organic 

 nitrogenous compound, but also an ex- 

 ample of the increased harmful effect 

 brought about by the addition of the other- 

 wise so beneficial nitrate. This is in strong 

 contrast to the ameliorating effect of ni- 



