Dec. IS, 1914 Assimilation of Colloidal Iron by Rice 209 



the dialyzed iron than in the ferric chlorid/ they assimilated less iron, 

 even in solutions containing three to five times more dialyzed iron than 

 ferric chlorid. It seems probable that the small amount of iron obtained 

 from the dialyzed iron was not colloidal iron but soluble iron. It is true 

 that the tests made of the dialyzed-iron preparation revealed little or no 

 ionized iron, but we must assume the presence of some soluble iron from 

 the chlorin content of the preparation. 



In view of the low availability of the dialyzed-iron solution it would 

 seem that the often-mentioned but questionable acid excretion of roots 

 was not operative, at least not in this unbalanced solution. With respect 

 to fineness of division and contact with the roots the colloidal iron was 

 especially favorable for assimilation by an acid if the roots had excreted 

 such. An apparent objection to the conclusion that colloidal iron is not 

 assimilable is the fact that dialyzed iron is sometimes used in nutrient 

 solutions and that in Von Crone's nutrient solution ferric phosphate is 

 emploj'ed. In such solutions, however, it is not at all certain that the 

 plants utilize insoluble iron compounds. In fact, from further work in 

 progress it appears that rice at least is capable of assimilating only solu- 

 ble iron in nutrient solutions. 



Aside from the question of the assimilation of colloidal iron, the pre- 

 ceding test is of interest in connection with the study of unbalanced solu- 

 tions. The fact that while some roots of the plant were developing well 

 in the balanced solution of the flasks A other roots of the same plant 

 were injured by the distilled water or ferric chlorid of the flasks B shows 

 that in case the toxicity of certain salt solutions or ordinary distilled 

 water is due to injury in the root cells by extraction of other electro- 

 lytes,^ this extraction takes place faster than the electrolytes can be 

 supplied from other parts of the plant. For in this case the roots in 

 flasks A had an abundance of the electrolytes to draw on. 



The idea that the toxicity of single-salt solutions is due to or accom- 

 panied by the penetration of the salts finds confirmation in the preced- 

 ing experiments. It is evident from Experiment III that the stronger 

 the ferric chlorid solution the less the root development in fhe solution, but 

 the greater the amount of iron absorbed (as shown by the top growth 

 which was dependent on iron absorbed). Osterhout ^ has shown by 

 electrical conductivity measurement that single-salt solutions penetrate 

 cells of the kelp, Laminaria. 



* The reduction of the toxicity of distilled water by colloids and finely divided solids has been frequently 

 noted. 



» True, R. H. Loc. cit. 



8 Osterhout, W. J. v. The permeability of protoplasm to ions and the theory of antagonisms. In 

 Sdeuce. n. s., V. 35, no. 890, p. 112-115, 1912. 



