1 62 THE AMERICAN MIDLAND NATURALIST 



which the iron is no more soluble, or at least is not more inter- 

 changeable with other bases such as Cu. . 



Although biochemical reactions may be efficient in changing 

 the soluble iron salts from the thermal water, into the non-soluble 

 iron hydroxide, the adsorbing effect of the cell walls plays a great 

 role: in fact, Fe or Cu ions may be fixed in a few minutes by 

 Baregine, and those parts which fix the metal most energically are 

 also those which show the greatest basophily. 



It seems therefore that Fe ions are at first adsorbed from the 

 solutions and then biochemically oxydized. 



4. Diatoms. 



Building of siliceous skeletons by Diatoms was compared by 

 Cohn to depositing of iron by Iron-bacteria. 



Indeed, we found that Syncdra affinis, growing in the Bassin 

 d'Arcachon, near to rusting iron pieces, had developed a rusty 

 color. Moreover,, we wers able to grow rusty Diatoms in very 

 weak solutions of Iron sulphates in sea water. These rusty Diatoms 

 yielded Prussian Blue, by treatment with hydrochloride ferrocyanide 



Here again we may turn to adsorption for an explanation; 

 Diatoms possess, inside of their siliceous skeleton, a very thin 

 pectic wall, which may adsorb metallic ions, and which we made 

 even to adsorb Cu. 



5. — Struggle for Bases from Soil to Plant. 



Most plants are in contact with the soil through the basophilous 

 pectic walls of their root-hairs. 



These walls compete for bases with the basophilous compounds 

 in the soil. 



Bases may be in excess in soils and then easily obtainable by 

 plants, or they may be strongly fixed by the basophilous complex 

 in the soil, such as humic acids, iron hydorxyde . . . the soil being 

 then termed "acid." Most plants thrive on the former soils, but 

 there are few able to live on "acid soils." The former plants have 

 been demonstrated to possess but feeble adsorbent power towards 

 Ca ions, while the latter have a high competing power for bases. 

 [i7-] 



3. — AciDOPHiLOus Adsorption. 



Some colloids, such as the basic gels: oxides of Z, Th, Al, La, 

 Zn, Be, Fe and Cr, or celluloses, adsorb the acid more quickly 



