116 Principles of Plant Culture. 



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 induced to start their buds soon 

 after jnaturity by exposing them to the sun a few days, 

 or by placing them for a like time in a refrigerator con- . 

 taining ice. By these means, the farmers of Tennes- 

 see 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 green house plants is toward the close of 

 the natural rest period. 



179. The Round of flant Life has now been traced, 

 from the first swelling of the planted seed, through the 

 development of the embryo into the plantlet, the pene- 

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

 the absorption and conduction of water with its food 

 materials in i-olution, co-operating with the sunlight 

 and carbonic acid in the mysterious laboratory of the 

 leaf, in building up the plant body into node and inter- 

 node, leaf, bud, branch, flower, fruit and seed; through 

 growth decline, leaf fall and winter sleep, to the re- 

 newed vigor of another springtime. 



In our study of the round of plant life, we have as- 

 sumed the environment to be favorable. But in the 

 practical culture of plants, we are constantly meeting 

 with adverse conditions of environment. Talent for 

 plant culture lies in the ability to discern these adverse 



