152 Journal of Agricultural Research vol. xx, No. a 



native of our northern cold-winter region which were tested went dor- 

 mant in fall or winter regardless of temperature. In comparing outdoor 

 plants with indoor plants of the same species the most that can be said 

 in favor of outdoor conditions is that dormancy progresses a little faster 

 in outdoor plants, evidently because their foliage is injured by freezing 

 weather, and they drop their leaves somewhat earlier than indoor plants. 



2. Trees and shrubs that are kept continuously warm during 

 the winter start into growth much eater in spring than those 

 that have been subjected to a period of chilling. 



In the late winter and early spring of 1910 I waited patiently, and 

 then impatiently, for my indoor plants to bloom, and at last I was forced 

 to realize that they never would bloom. When compared with plants of 

 the same kind that had been outdoors during the winter and had been 

 brought into the greenhouse in early spring, the difference was astonish- 

 ing. The outdoor plants burst into leaf and flower luxuriantly, while 

 the indoor plants remained completely dormant and naked. The exper- 

 iment was repeated many times and with various species of plants, some 

 of which may be used in illustration. (See PI. 20, B; 21 ; 22, A.) 



At first it was supposed that the plants needed to be frozen to start 

 them into growth, but a single freezing proved not to be effective. And 

 then it was found that the dormant plants would start into growth 

 without any freezing whatever. It was necessary only that they be 

 subjected to a period of prolonged chilling, usually two or three months, 

 at a temperature a few degrees above freezing. 



If plants are kept continuously in a warm place without chilling, the 

 dormant condition often continues for an extraordinary length of time. 

 In some instances plants have remained dormant for a whole year under 

 conditions of heat, light, and moisture that ordinarily would make the 

 same plant grow with the greatest luxuriance. 



3. The stimulating effect of cold is limited to such portions 

 of the plant as are subjected to the chilling. 



The conspicuous difference in spring growth between chilled plants 

 and plants not chilled has already been shown. These differences, 

 furthermore, can be produced experimentally upon different parts of 

 the same plant. Plants thus treated present a very curious and remark- 

 able appearance, as shown in Plate 22, B, and Plate 23. 



On February 3, 1912, a blueberry plant (PI. 22, B) 44 inches in height, 

 which had shed its leaves and become dormant in a warm greenhouse 

 maintained at a temperature of 6o° to 70 F., was subjected to the 

 following experiment: It was repotted in a 7-inch pot and set in the south 

 end of a greenhouse at the temperature already mentioned. A small 

 opening was made in the glass, and through this opening one of the two 

 stems of the plant was pushed. The open space about the stem where 

 it passed through the glass was carefully plugged with moss. During 



