No. 574] 



VARIATION 



597 



should choose those varieties which he can grow to the 

 highest degree of perfection under his conditions' of soil 

 and climate. The causes of variation are summarized, 

 giving special attention to the influence of temperature as 

 a factor in the distribution of apple varieties. The north- 

 ern limit is regarded as fixed by the lowest temperature 

 which the tree will stand, while the effect of summer 

 heat upon the development of the fruit is looked upon as 

 limiting the distribution southward. The elongation 

 of the fruit was found to be correlated with a low tem- 

 perature for two or three weeks after blooming. A low 

 summer temperature produces greater acidity, higher 

 content of insoluble solids, greater astringency, smaller 

 size, and scalding in storage. The extent of coloration 

 was regarded as decreasing from the center of distribu- 

 tion in passing either north or south, while the intensity of 

 coloration was considered greatest in high latitudes and 

 altitudes. Excessive summer heat results in uneven 

 ripening, premature dropping, rotting on the tree, poor 

 keeping quality, lack of flavor, mealiness, less intense 

 color, and smaller size. For each variety there is a mean 

 summer temperature at which it reaches its highest de- 

 velopment. 



It will be noted that Shaw's method of investigating 

 the problem consisted in securing fruit for comparison 

 from widely separated localities and attempting to corre- 

 late the various characters with the conditions of produc- 

 tion. Stewart, on the contrary, confined his study to 

 apples grown in one locality and noted the effect of modi- 

 fying one at a time those factors within his control. This 

 is the more scientific method of procedure, but has the dis- 

 advantage that the variations are far less striking and a 

 smaller number of factors can be studied. An account of 

 Stewart's experiments and the results so far attained is 

 found in the reports of the Pennsylvania station since 

 1907. These papers deal largely with the effect of fer- 

 tilizers and different cultural methods on the yield, color, 

 size and growth of the apple. The various factors influ- 



