10 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol 



part of the coatings of the grains. 1 So far as culture solutions 

 are concerned, however, it seems to us that the action of the 

 colloid as a protection against precipitation of tricalcium 

 phosphate is a simpler explanation. 



In considering the work of Kaserer and of Remy and Ros- 

 ing, particularly of the latter, the fact must not be lost sight 

 of that the terminology used by them with respect to solutions 

 is very loose in the light of modern chemistry. The "ferric 

 hydroxide solution" of Remy and Rosing is, of course, a col- 

 loidal suspension of hydrated ferric oxide, and as such it 

 might easily possess the property of a protective colloid and 

 prevent the flocking out of phosphates in the culture medium. 

 Kaserer 's postulation of a silicophosphate as a chemical com- 

 pound is unwarranted. It is much more likely that his "iron 

 aluminium silicophosphate" is a colloidal suspension of vary- 

 ing composition and stability carrying with it some tricalcium 

 phosphate in colloidal suspension. 



As concerns Bottomley's results, it has already been men- 

 tioned that he considers the benefit observed by him to be due 

 to compounds containing phosphorus in the organic form. Re- 

 garding the results obtained by Bonazzi with mechanical agi- 

 tation, it is clear that ' ' auximones ' ' and "rare elements" are 

 eliminated, although "oxygen carriers" and the "adsorption 

 of gases" might really have the same action as that of the 

 shaker. It seemed more probable to us that the precipitate 

 which formed in the medium contained phosphates absolutely 

 essential to the development of the microorganisms, and that 

 the agitation hastened the restoration of the concentration 

 of the solution in the equilibrium which exists between this 



solid phase and the nutrient solution as the materials are 



1 Sohngen considers the possibility of adsorption phenomena being operative. 

 For instance, he says: 'The equilibrium between the concentration of the dis- 

 solved substances in the soil water and the nonorganized colloids is therefore 

 continually disturbed in consequence of the metabolism of the organized colloids. 

 Yet the concentration of substances in the soil water is maintained more nearly 

 constant than in a medium without colloids, for the reason that the nonorganized 

 colloids give up again the compounds obtained from the soil water because of 

 the new state of equilibrium between the concentration in the liquid and the 



colloid There is therefore a continual exchange of assimilable 



compounds between the organized and the nonorganized colloids, by virtue of 

 which the mass of the nonorganized colloids serves as a storehouse with assimi- 

 lable compounds, which is daily filled, and out of which the organized colloids 

 regularly feed.' 



