106 THE APPLE 



found to exist above certain concentrations, often in a very marked 

 degree, and the neutralizing power of other bases, especially lime, 

 has been shown always to follow their addition. The strong toxic 

 action of copper salts in solution has long been known and utilized 

 in spray materials. The neutralizing action of lime additions in these 

 cases also is significant and may be similar to its action in nutrient 

 solutions. 



As in the case of magnesia, the relation of lime applications 

 to maturity in plants and to the fertilization of orchard fruits is 

 apparently not definitely known. 



Magnesium. This element is required in the development of 

 all plant parts, but is considered especially important in the forma- 

 tion of seeds and proteins. Its distribution and importance is 

 apparently similar to that of potassium. It can perform its proper 

 function, however, only in the presence of calcium salts, since, 

 with the exception of very few plants, it is strongly toxic in all 

 other cases. 



The action of magnesium is indirect ; that is, it does not enter 

 directly into the composition of plant parts or tissues, but apparently 

 serves only as a carrier of the phosphorus needed in their formation. 

 This theory is strengthened by the fact of the relatively easy de- 

 composition of the secondary magnesium phosphate into territory 

 and free phosphoric acid, a dissociation which would naturally im- 

 mediately precede assimilation. Magnesia is found always to increase 

 when rapid development is taking place, and comparatively little 

 of it will serve for extended physiological operations, a fact which 

 serves to corroborate the theory just stated. 



In leaves and wood the magnesia content is always noticeably 

 lower than the lime content, while the reverse is true of seeds 

 and fruits (see tables, p. ioo). Magnesium also migrates strongly 

 to the growing parts, in general " following the proteids, like the 

 phosphates." Its exact relation to fruit development is not known, 

 though the results of the experiment in Massachusetts suggest 

 its possible value in this connection. The relatively high amount 

 present in fruits, as well as its apparent relation to phosphatic 

 compounds, is also suggestive. It seems that nothing is known 

 concerning its relation to the hastening or retarding of maturity 

 in crops. 



