COLD AND GROWTH OF PLANTS — COVILLE. 2S3 
of the same plant. Plants thus treated present a very curious and 
remarkable appearance, as shown in plates 6 and 7. 
On February 3, 1912, a blueberry plant (pi. 6) 44 inches in height, 
which had shed its leaves and become dormant in a warm green- 
house, maintained at a temperature of 60° 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 men- 
tioned. A small opening was made in the glass, and through this 
opening was pushed one of the two stems of the plant. The open 
space about the stem where it passed through the glass was care- 
fully plugged with moss. During the rest of the winter the plant 
remained in the same position, the pot and the stem shown at the left 
in the illustration continuing in the warm temperature of the green- 
house, while the stem at the right, projecting through the glass, was 
exposed to the rigors of winter, with its alternate freezing and thaw- 
ing. The illustration, from a photograph made April 18, shows that 
when spring came the outdoor branch started into normal growth 
while the indoor branch continued dormant. 
A second illustration (pi. 7) shows a modification of the first ex- 
periment. In this case the plant was set on a shelf outside the green- 
house and a single branch was passed through the glass wall into 
the warm interior. When spring came it was this interior branch 
that remained dormant, all the outside branches putting out leaves 
promptly and normally. 
From a comparison of the two experiments it is evident that the 
difference in behavior of the indoor and outdoor branches could not 
have been caused by any special action of the root system, for in one 
exj^eriment the roots were inside, in the other outside. It is clear 
that the causes that stimulated growth in the exposed stems operated 
in the stem itself, not in the roots. This principle is still further 
exemplified and confirmed by the behavior of cuttings taken from 
blueberry plants in the first stages of their dormancy. Such cut- 
tings if kept warm continue their dormancy into late spring or sum- 
mer, but if chilled for two or three months they start into growth at 
the normal time in early spring. 
It should be stated here that the difference in the amount of light 
inside and outside the greenhouse had nothing to do with the stimu- 
lation to growth, for chilled plants are ready to start into growth 
promptly whether the chilling is clone in the full light of an outdoor 
situation, or in the partial light of a greenhouse, or in the complete 
darkness of an ordinary refrigerator. 
4. The stimulating effect produced on dormant plants hy cold is 
intimately associated with the transformation of stored starch into 
sugar. 
