47 



the starch, and another the impossibility of forming in the growing 

 parts new plastids and chloroplasts, which produce starch from sugar. 



The writer's view, according to which lime is required in the com- 

 pounds which build up nuclei and chromatophores, explains not only 

 the failure to increase these organoids, but also that to produce diastase 

 when line is absent. Enzyms are secreted from the nuclei, as Hofer 

 has shown with amceba?, and therefore if the nuclei can not be normally 

 formed for want of lime enzym formation also may stop. However, this 

 latter explanation does not seem to apply for the initial pathological 

 stage, since Raumer and Kellerman observed that in Fhaseolus multi- 

 florus sugar also was formed from starch for a ceitain period when lime 

 was deficient, hence diastase was probably present. 



In this case the upper part of the stem was devoid of starch and 

 seemed to be incapable of forming starch from the sugar present. This 

 accumulation of sugar prevented any further solution of starch in the 

 lower parts. 



The intensity of starch transportation depends essentially on two 

 factors, (1) the saccharifying activity, and (2) the starch-forming 

 activity of the plastids in other parts of the plants. 



Further investigations in this direction would be very desirable. 

 They would perhaps also show differences between the action of 

 chlorids and that of lime in regard to the transportation of starch. 

 Finally, since a deficiency of lime, like the absence of phosphoric 

 acid, potassa, or magnesia, stops the formation of new cells, an accumu- 

 lation of proteins may result, and indeed such a case was observed by 

 Stock, the crystalloids increasing in number when lime was deficient.^ 



THE PHYSIOLOGICAL ROLE OF MAGNESIUM SALTS. 



It has already been pointed out that magnesium salts are especially 

 important in the formation of seeds, but they are also required by all 

 other parts of plants, and especially in the process of development. The 

 amount of magnesia taken up by crops varies considerably. For 

 example, an average crop of wheat will take up 8 kilos per hectare, a 

 crop of leguminous plants 12 kilos, and a crop of tobacco as much as 43 

 kilos. It has also been pointed out that magnesium salts can fulfill 

 their nourishing functions only in the presence of calcium salts, while 

 in the absence of calcium salts they even exert an injurious action.^ 



In studying the questions as to what the nourishing function of mag- 

 nesium salts is and why they can not be replaced physiologically by 

 calcium salts, the probable answer is found in the well-known property 

 of the magnesium salts to easily undergo dissociation, as the writer 

 pointed out some years ago.^ Magnesium salts are easily hydrolyzed, as 

 is shown in the preparation of chlorid or carbonate of magnesium in the 



1 Bot. Centralbl., Vol. LIII, p. 83. 



2 Only the lowest algt© and fungi are exceptions (p. 44). 



3 Flora, 1892, p. 286. 



