154 



FUNDAMENTALS OF FRUIT PRODUCTION 



Though magnesium is necessary for plant growth, it is not required 

 in large quantities and so far as is known all soils contain sufficient amounts. 

 Certainly no data are available showing the necessity of fertilizing fruit 

 plantations with magnesium-carrying compounds. 



CALCIUM 



Calcium is for the most part absent from the growing points and from 

 embryonic tissues generally and it accumulates in all tissues with age. 

 This indicates that calcium is utilized in ways very different from the 

 other essential elements, a surmise substantiated by the fact that it is not 

 necessary for the growth of fungi. 



It is found organically combined in calcium oxalate crystals, in 

 calcium peCtate of the middle lamella which holds adjoining cells together, 

 in salts of arable acid, in the globoid of aleurone grains and in the antho- 

 cyan pigments. It is prevalent also as calcium carbonate. 



Seasonal Distribution of Calcium. — Calcium differs from the elements 

 previously discussed in its seasonal history in the tree. It has been 

 mentioned that where potassium is present in large amounts, calcium 

 is usually present in small amounts and vice versa. 



In Buds and Leaves. — The calcium content of buds Is not great as compared 

 with that of other plant tissues. Leaf buds have more lime, but less potassium, 

 than fruit buds. In percentages of dry weight, the Ume content of leaf buds has 

 been found to be 1.364 per cent, in the cherry and 2.365 per cent, in the plum; 

 that of fruit buds was 1.113 per cent, in the cherry and 1.761 per cent, in the 

 plum.i^^ Very heavy deposits of calcium oxalate have been found in resting 

 fruit buds, the amount decreasing after growth begins. As leaves grow older 

 their percentage lime content increases, as Table 47 shows. The absolute lime 

 content increases also (cf. Table 48). 



Table 47. — Lime Content of Leaves^^^ 

 (In percentage' of dry weight) 



Apple 



Pear 



Cherry 



Plum 



May 9. 

 May 14. 

 May 18. 

 June 22. 

 Aug. 29. 

 Sept. 30 

 Oct. 2.. 

 Oct. 15. 



1.186 



2.166 

 2.762 



3.723 



0.754 



1.977 

 3.147 

 3.473 



1.511 



2.699 

 3.987 

 4.558 



1.025 

 3.512 

 4.591 

 5.696 



