1 60 Journal of A gricultural Research vol. xx , no. 2 



is required. The practice of gardeners and nurserymen known as the 

 "stratification " of seeds is probably to be explained as in reality a process 

 of chilling. 



As a single example of the application of the principle of chilling let 

 me cite the case of the blueberry. For several years we have been 

 trying at the Department of Agriculture to domesticate this wild plant. 

 We have raised many thousand hybrids and have set them out in waste 

 sandy lands in the pine barrens of New Jersey ( PI. 33, A) . We have grown 

 the bushes to fruiting age and have brought them into highly productive 

 bearing (PI. 33, B). We have made them fruit so lusciously and so abund- 

 antly that they have brought returns to the grower at the rate of more 

 than $1,000 an acre. In a word, we have changed the blueberry from a 

 small wild fruit the size of a pea to a fruit the size of a Concord grape, and 

 we have made its culture a profitable industry. (See PI. 34, 35.) These 

 things we should not have been able to do unless we had first worked out 

 the principle of chilling, an understanding of which was essential to our 

 work of breeding and propagation. 



In conclusion, I wish to express the opinion that the chilling of dormant 

 trees and shrubs of temperate climates as a prerequisite to their resump- 

 tion of normal growth in the spring ought to be recognized in books on 

 plant physiology as one of the normal processes in plant life. These 

 works should contain chapters on chilling, just as they now contain 

 chapters on other fundamental factors and principles relating to the life 

 history of plants. And especially in books on plant physiology in relation 

 to agriculture should the subject of chilling be dealt with in detail, for 

 when in the pursuit of agriculture we take plants from one part of the 

 world to another, or undertake to grow them out of season, or attempt 

 to propagate them in quantity by grafting or by other processes unknown 

 in nature, we are greatly handicapped and limited in our operations if we 

 do not understand the principles of a process so widely existent in nature 

 and so indispensable to a large proportion of the plants of temperate 

 agriculture as the process of chilling. 



