40 



of pliosi)bate to a trace inultiplicatiou cau be very inucli retarded or 

 stopped altogether, while albumin formatiou may go ou; lieuce in this 

 case an accumulation of albuniin'takes place either in the cell sap or in 

 the cytoplasm or in both. 



These conclusions can be very easily verified by studies with Spiro- 

 gyra, for which the bicarbonate, obtained by dissolving magnesium 

 carbonate in water charged with carbonic acid, is a very favorable form 

 of magnesium. Thus a most energetic growth was observed with the 

 following composition : 



Per iiiille. 



Magui'sinm biearboiiate 0. 5 



Magnesium sulphatf 1 



Calcium nitrate .5 



Mouopotassium phosphate .05 



Potassium nitrate .2 



Ferrous sulphate X^ace. 



The supposition that the favorable action of the magnesium bicar- 

 bonate consists sinii)ly in a "neutralization of acids" formed in the 

 process of metabolism, (;an not be correct, since a substitution of an 

 eqnalamount of calcium bicarbonate by no means shows thesame benefi- 

 cial influence, and besides in this case the above culture solution would 

 contain such an excess of lime over magnesia that the assimilation of 

 phosphoric acid might be retarded, involving a slower development. 



The foregoing makes it intelligible why in the absence of magnesium 

 salts the multiplication of cells is stopi)ed, the nucleus not being able 

 to in(;rease to that jjoint where <livision sets in. In the mixture of dif- 

 ferent salts occurring in plants there is sufficient opportunity for mag- 

 nesia to combine with phosphoric acid, and the secondary magnesium 

 j)hosphate thus formed can, in passing into the tertiary salt, yield some 

 free acid. The tertiary salt remaining can easily be redissolved by 

 weak organic acids, and thus yield again the secondary phosphate, 

 which may in turn be utilized for the assimilation of phosphoric acid. 

 This explains why germinating seeds and rapidly growing parts gener- 

 ally develop an acid leaction. 



The rapidly proceeding cell division requires the most favorable con- 

 ditions for the assimilation of phosphoric acid. One of these consists 

 in utilizing the same amount of magnesia over and over again. Where 

 an abundance of magnesium salts is present, however* as in most cul- 

 ture solutions of bacteria, the reaction does not need to be acid to insure 

 a rapid assimilation of phosphoric acid. 



Thus far few authors have expressed any view as to the primary 

 functions of magnesia. Eaumer observed that Phaseolus mtdtijforus, 

 grown in culture solutions without magnesia, reached 1 meter in height, 

 after which the internodes stopped stretching, but thickened abnor- 

 mally. The new leaves also remained small and ceased to x)roduce 

 chlorophylP — an interesting case of chlorosis, which disease may be 



1 Hoppe's chlorophyllan contains 0.34 per cent magnesia, but this product is now 

 declared to he a mixture. 



7478~No. 18 4 



