HORTICULTURE A GREAT GREEN CARPET 43 1 



and are therefore successful in Northern regions, whereas other varieties 

 form fruit buds in shorter days and so are adapted to other regions. 



Further, plants are grown in large constant-temperature tanks where the 

 root temperature can be properly maintained. With a root temperature of 

 45 °F., strawberry plants require less fertilizer for the production of the same 

 amount of dry weight than they do at 75 °F. Further, there is a difference in 

 soil-temperature requirements between varieties. When it is realized that 

 there may be as much as 30 degrees difference between the temperature of 

 soil under mulch and under clean cultivation, such information has real 

 significance. 



Another recent contribution to orcharding has come from studies involving 

 the growing of fruit-tree rootstocks at controlled root temperatures. Until 

 recently, there has been great difficulty in determining the natural adaptation 

 of several of the clonal Mailing apple rootstocks. Now it is found that certain 

 of these rootstocks, such as Mailing IX, produce new roots even at root 

 temperatures of 44 °F., whereas they disintegrate in soil temperatures of 

 77 °F. and higher. On the other hand, French Crab seedling rootstocks pro- 

 duce no new roots at 44°F., but grow luxuriously at 77°F. or higher; and 

 Mailing VII seems adapted to a wide range of soil temperature, producing 

 roots at 55 °F. as well as at 77^F. The results explain the growing popularity 

 of Mailing IX in the North and of Mailing VII as a widely adapted apple 

 rootstock in the United States and the abandonment of Mailing IX in South- 

 ern regions in place of French Crab rootstocks which will tolerate high soil 

 temperatures. 



Temperature studies of this kind may also reveal much regarding adapta- 

 tion of varieties, responses to plant regulators for blossom thinning and 

 pre-harvest drop, coloring of fruit, and development of good finish in associa- 

 tion with various spray materials. 



Nutrition and fertilizers. As regards fertilizers and fruit-tree nutrition, 

 the case no longer rests with chemical analysis of the soil alone. Analyses 

 of the tissues of the plant have been found valuable to supply additional in- 

 formation. The use of nitrogen has become fairly well standardized with 

 either fall applications or early spring applications. But, as dependence has 

 been placed largely upon nitrogen, other materials have been found of in- 

 creasing importance, such as phosphorus and potassium. Various other de- 

 ficiency troubles also have been identified and have been corrected by the 

 application of specific materials, as the little-leaf disease of citrus with zinc 

 and the internal corking of apples with boron. The trend now is to use leaf 

 analysis by the spectrographic method for large-scale surveys of nutritional 

 status and as the basis for rapid determination of plant needs. Balance be- 

 tween various elements is receiving considerable attention, as, for example, 

 the relation between calcium and boron, in which boron aids in the efficient 

 use of calcium. 



