PHYSIOLOGICAL CHARACTERS 85 



Most of the evidence seems to show that heredity is complete 

 in plants propagated from vegetative parts, and that fruit- 

 growers may expect a variety grown under the same conditions 

 to behave indefinitely as did the original plant. The variations 

 which appear in varieties are for the most part due to environ- 

 ment and come and go with changes. 



Whether or not varieties are permanent is most important to 

 systematic pomologists. If plants are continually changing or 

 being changed, the task of classification is much more difficult, 

 if, indeed, such instability would not make it worthless. In 

 systematic pomology there is conclusive proof that varieties 

 are not changing except in the rare cases of bud-sports ; thou- 

 sands of varieties of fruits which have passed through many 

 generations of vegetative propagation are today as they were 

 at their time of origin. 



126. Correlations. — Some of the organs of plants are so 

 related to each other that a modification in the structure or 

 function of one brings a change in another. Such phenomena 

 are called correlations. The nature of these linkages of organs 

 and functions is obscure, but their existence is important and a 

 search for them is imperative to those w^ho describe plants, as 

 knowledge of correlations is most helpful to all who work to 

 improve plants. Correlations are not common phenomena, but 

 the occasional rewards to those who seek them make the search 

 fascinating. 



To illustrate the importance of correlations in pomology and 

 plant-breeding a few examples may be given : Luxuriance of 

 foliage and fruit-bearing are mutually antagonistic; high color 

 of fruits in pomes and luxuriant foliage are antagonistic. Black 

 or red color in Labrusca grapes is usually associated with a 

 foxy odor and taste. Short bunches of fruit in all grapes are 

 correlated with short joints in the canes. Varieties of peaches 

 with glandless leaves are most susceptible to leaf mildew. The 

 color of the inside of the calyx-cup of peaches is correlated with 

 the color of the ripened fruits ; varieties having calyx-cups with 

 green inner surfaces bear white-fleshed peaches, orange inner 

 surfaces, yellow-fleshed peaches. Reniform glands in peaches 

 are correlated with ' crenate margins in the leaves ; globose 

 glands, wdth serrate-crenate glands. 



