-7- 



That large quantities of soil fertility go up in smoke when plant 

 residues are burned? Nitrogen, which entered the plant from the soil, goes 

 into the air as a gas while only such mineral elements as calcium and potas- 

 sium remain in the ash. We have yet to see a good orchard in which the owner 

 makes a regular practice of burning the grass instead of allowing it to remain 

 to enrich the soil. 



That at least 5 grains of pollen must reach the stigma of each apple 

 blossom to bring about the development of a normal, well formed apple? The 

 pistil of an apple blossom is a 5-parted affair and unless one pollen grain 

 reaches each part of the divided tip a normal seed will not develop in each 

 of the five sections of the ovary or core. If a pollen grain is placed on 

 one of the stigma segments only, the resulting fruit, if it develops at all, 

 will be lopsided. More than likely it will drop from the tree in the so- 

 called June drop when the apples are competing with each other for water 

 and other things needed in their development. 



A CORRECTION ^- In an April Fruit Notes article "DDT in 

 Oriental Fruit Moth Control," two errors should be noted, 

 as follows* Line 8 should read "...» about June 1, July 15, 

 and September 1," The last sentence in the next to the 

 last paragraph should read ".... and 3 applications of DDT 

 appear safe «...." 



MAGNESIUM IN THE APPLE ORCHARD 



(Following is part of a paper written by Lawrence Southwick, formerly 

 of the Pomology Department and now with a large chemical concern.) 



Magnesium is one of the mineral elements essential to normal plant 

 nutrition. As early as 1840, Liebig considered magnesium to be an essential 

 element since it was found in considerable amounts in plant ash. Willstatter 

 in 1906 first showed that magnesium is one of the constituents of chlorophyll 

 and now it is recognized to be the key element in this substance which is so 

 essential to green plants. With the aid of chlorophyll, the energy from the 

 sun is utilized to build up plant tissue which, directly or indirectly, has 

 supplied man with most of the necessities and luxuries of life. 



Green chlorophyll contains 2,7 per cent of magnesium in its chemical 

 makeup. However, since only about 10 per cent of the m.agnesium required for 

 normal plant growth is contained in the chlorophyll, this element probably 

 has other essential functions. Along with nitrogen, potassium, phosphorous, 

 calcium, and sulfur, magnesium is a major nutrient element and is utilized 

 in considerable quantity by orchard trees as well as other crop plants. When 

 the supply of this element is insufficient, deficiency in crop plauits such 

 as tobacco, corn, potatoes and some vegetables has been a problem for a num- 

 ber of years in Atlantic coastal areas. In Florida magnesium requirements of 

 citrus trees have not been satisfied by native soil supplies and fertilization 



