430 TUKEY 



tion. For example, A^-wz-tolylphthalamic acid will increase blossom number 

 in the tomato and naphthaleneacetic acid is used commercially in Hawaii 

 to control flowering in the pineapple. 



More recently, the gibberellins have been shown to affect flowering in 

 several plants. Applications of gibberellic acid to some biennial plants, as 

 the carrot and the collard, have resulted in these plants developing as an- 

 nuals. 



Environmental adaptation of horticultural plants. Matters of soil, 

 location, and site are perhaps now as well understood as any aspect of Horti- 

 culture. It is known that certain areas are suited to peaches, others to pears, 

 potatoes, celery, and so on. Yet too much of this has been learned by bitter 

 experience. The new technique is to study adaptation by controlled experi- 

 ments and to be able to predict. Thus, branches of trees are enclosed in 

 cooled and in heated chambers as desired to simulate different climatic con- 

 ditions. It is found by this means that sour cherry fruits grow rapidly at high 

 night temperatures for a period immediately following full bloom, but that 

 they develop slowly, with low quality and with poor color, if the night tempera- 

 tures are high late in the season as the fruit is maturing. Accordingly, it would 

 seem that the sour cherry would be best suited to an environment where 

 early summer temperatures were relatively high, followed by cool night 

 temperatures prior to harvest. That the sour cherry industry is confined 

 largely to Michigan, Wisconsin, and New York is thus seen to be more than 

 chance. 



Delayed dormancy of fruit trees is another problem in adaptation which 

 has been met by research. Considerable distress has been experienced in 

 Southern sections in some seasons with delayed and scattered foliation and 

 blossoming and attendant financial reverses. The answer has been found 

 in varying hours of chilling required by different varieties of peaches, so that 

 varieties which are adapted to the long chilling provided by Northern winters 

 do not break dormancy in Southern regions. Varieties of tree fruits for the 

 South are now catalogued as to the amount of chilling required to break 

 dormancy. Further, breeding programs recognize these facts and have suc- 

 cessfully developed varieties of peaches adapted to southern California and 

 to other Southern regions. The shift of peach production southward even into 

 Florida is a direct outcome of this type of research. 



The bulbing of onions, the tubering of potatoes, the bolting of celery and 

 lettuce, and the adaptation of certain floricultural crops and woody orna- 

 mentals to various geographical locations are now better understood and 

 predictable. Recently it has been shown, for example, that the Northern 

 distribution of certain azaleas and rhododendrons is limited in nature by 

 the fact that in the relatively longer summer day lengths of Northern latitudes, 

 these plants do not mature properly and are subject to killing by winter cold. 

 Also, some varieties of strawberries tend to form flower buds in long days 



