Decline of Growth and the Rest Period. 113 



callusing (73) and the transfer of food may make some 

 progress before the final planting. 



179. The " Turn of the Year." Toward the close of the 

 dormant season, vegetation, as if benefited by the rest, is 

 prepared, to start with renewed vigor, even at moderate 

 temperatures. Buds, that remained dormant during the 

 latter part of the previous summer, push into growth 

 with the first warm days of spring, and many seeds, that 

 could not be induced to germinate the preceding autumn, 

 start with vigor as soon as the soil is sufficiently warm. 



The cause for this energetic resumption of plant growth 

 after the rest period is not well understood, but exposure 

 to cold, in the case of temperate plants, and to prolonged 

 dryness in that of tropical ones, doubtless explains it in 

 part, for it is well known that potato tubers may be in- 

 duced to start their buds soon after maturity by exposing 

 them to the sun a few days, or by placing them for a like 

 time in a refrigerator containing ice. By these means, 

 farmers of Tennessee grow a second crop of potatoes in 

 the latter part of summer and during autumn. 



Plants under glass usually thrive better after mid- 

 winter than before, and the most favorable time to plant 

 seeds of greenhouse plants is toward the close of the 

 natural rest period. 



180. The Round of Plant Life has now been traced, from 

 the first swelling of the planted seed, through the de- 

 velopment of the embryo into the plantlet, the penetra- 

 tion of the root into the dark and damp soil cavities, the 

 absorption and conduction of water with its food mate- 

 rials in solution, co-operating with the sunlight and car- 

 bonic acid in the mysterious laboratory of the leaf, in 



