290 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1919. 
ness of this refrigerated frame in experimental work with plants 
was so great that another similar equipment was installed in 1918. 
With the aid of this apparatus many of the experiments described 
in this address have been carried on or verified, as well as other 
experiments of a related character. For example, at ordinary summer 
temperatures many kinds of seed will not germinate but remain 
dormant until death overtakes them. Under the influence of chilling, 
however, these seeds are stimulated to prompt germination. (See 
pi. 18.) 
The experiments thus far made indicate the importance of a much 
wider use of the principle of chilling in many lines of experimenta- 
tion bearing on the improvement of horticultural and agricultural 
practices. I commend the subject of chilling to experimenters in 
these lines, an^ I wish to call especial attention to the desirability 
of determining proper temperatures for the storage of seeds, bulbs, 
cuttings, and grafting wood; proper temperatures for the treat- 
ment of plants which are to be forced from dormancy to growth at 
unusual seasons ; and proper temperatures for the storage of nursery 
stock, so that the nurseryman may have plants in proper condi- 
tion for shipment on any date he desires. (See pis. 19 to 23.) 
The whole question of the effect of chilling on herbaceous peren- 
nials is an open field. 
An understanding of the process of chilling explains the reason 
of some of the practices of gardeners, which they, as well as botanists, 
have erroneously ascribed to the need of " resting." What a gardener 
calls " resting " is often in reality a period of chilling, characterized 
not by physiological rest, but by pronounced internal activity. Rest 
alone would not, in the case of our cold-climate trees and shrubs, ac- 
complish the purpose the gardener has in mind. It is chilling, not 
rest merely, that is required. The practice of gardeners and nur- 
serymen 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. (See pi. 24.) 
We have grown the bushes to fruiting age and brought them into 
highly productive bearing. (See pi. 25.) We have made them fruit 
so lusciously and so abundantly 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 pis. 26 and 27.) These things we should not 
