16 RELATION OF LIME AND MAGNESIA TO PLANT GROWTH. 
THEORETICAL DISCUSSION OF THE FUNCTIONS OF LIME AND. 
MAGNESIA. 
The physiological role of lime and magnesia was fully discussed in a 
previous bulletin,’ hence a few lines touching the chief points will 
suffice here. The lime is, according to the theory of the writer, neces- 
sary for the formation of certain calcium compounds of nucleo-proteids 
required in the organized structures of nuclei and chlorophyll bodies, 
while the magnesia serves for the assimilation of phosphoric acid, since 
magnesium phosphate can give up its phosphoric acid more easily than 
any other phosphate that occurs in plant juices. While calcium is fixed 
in the organized structure, magnesium is movable, since it serves mainly 
in the form of secondary phosphate as carrier of assimilable phosphoric 
acid, which rdle can be repeated various times. 
It follows from this theory that, in the case of an excess of lime 
being taken up, the assimilation of phosphoric acid will be rendered 
more difficult, since this acid will chiefly combine with the lime, and 
the chances for the formation of magnesium phosphate will thus be 
diminished. The effect will be the same as if the amount of available 
pkosphorie acid in the soil were lessened—that is, the growth of the 
plant will be retarded and even starvation phenomena may set in. 
Many plants avoid this evil effect of an excess of lime in the juices by 
the precipitation of a part of the lime as oxalate, as mentioned above, 
while others” secrete it as carbonate, contained also in cystoliths. 
If, on the other hand, magnesia is taken up in considerable excess 
over lime a poisonous action is observed. Plants succumb soon when 
placed in diluted solution of magnesium salts and no other, but calcium 
salts can prevent this effect. In fact, magnesium salts can exercise 
their nutritive functions only in presence of a sufficient amount of 
calcium salts. The plants can not, as with lime, turn an excess of mag- 
nesia into an insoluble form and thus render it innocuous. Only in 
certain cases may the formation of globoids or of insoluble magnesium 
protein compounds come into consideration. 
The injurious action of magnesium salts has been previously explained 
by the writer,’ as follows: The calcium nucleo-proteids of the organ- 
ized structures are transformed by the presence of soluble magnesium 
salts into magnesium compounds, while the calcium of the former 
enters into combination with the acid of the magnesium salt. By the 
transformation of the organized calcium nucleo-proteids into magnesium 
nucleo-proteids the capacity for imbibition will change, which must 
lead to a disturbance in. the structure which will prove fatal. Only 
the simultaneous presence of dissolved lime salts can prevent this 
1Bul. No. 18, the physiological réle of mineral nutrients, U. 8. Dept. Agr., Div. 
Veg. Phys. and Path., pp. 28, 37, 42, 47, and 60. 
* Saxifragineze, Plumbaginez, and some ferns secrete calcium carbonate on their 
epidermis. 
* Bul. No. 18., U.S. Dept. Agr., Div. Vez. Phy-. and Path. 
