1917] Lipman-GericTce : Smelter Wastes and Barley Growth 533 



dry weight produced is concerned, did any of the treated pots 

 produce so low a yield as the control pots, when averages are 

 considered. The great immunity to chlorine which the plants 

 in the third crop of this series manifest is very difficult to 

 explain. In general, however, the changes in the effects of 

 MnClg from one crop to another are much the same in nature 

 as those of the MnSO^ series which have been discussed more 

 in detail above. It looks obvious that we are dealing primarily 

 in both manganese series with the effects of the kation rather 

 than with those of the anions, though, to be sure, specific effects 

 of the latter do not seem to be wanting. The balance of the 

 data presented in table Xc speaks for itself. 



COMPARISON OF OUR RESULTS WITH THOSE OP 

 PREVIOUS INVESTIGATORS 



It is quite unnecessary to review in detail the results of the 

 numerous investigations which bear on the subject in hand, par- 

 ticularly those relating to copper and its influence on living 

 organisms. Although, therefore, we are herewith citing a very 

 extensive bibliography, we shall make no attempt at reviewing 

 all of the investigations which have been carried out. It does 

 seem desirable, however, to compare in general the results of 

 our investigations with those of other researches in the hope that 

 we may thereby arrive at some definite understanding, now that 

 so much experimental work has been accomplished, as to the 

 real status of the salts in question in the realm of plant physi- 

 ology. In order to simplify such discussion, we shall take up 

 the different so-called toxic metals separately. 



Copper Sulfate 

 As pointed out above, the bibliography on the subject of 

 copper and its effects on plants is very extensive. One needs 

 but to turn to the complete reviews of it by Czapek,^ Pfeffer,** 



8 Biochemie der Pflanzen, vol. 2, p. 910, Jena, 1905. 



9 Pflanzenphysiologie, vols. 1 and 2, Leipzig, 1897 and 1901. 



