OF GROWTH IN TREES. 93 



exhausted vitality of the plant has retired. Then comes 

 the sleep of Winter, when forest tree and lowly flower alike 

 repose, till the onward march of Nature brings back to 

 earth the heat and light of Spring, re-awakens the dormant 

 life-energies in the seed, which slowly commences the 

 same instructive and ever deeply-interestyig life move- 

 ments. 



In forest trees, or woody perennials, there is the same 

 continual change from a state of rest to that of motion. 

 As the tree grows, the life-movements forward are accele- 

 rated and then retarded, year after year. These fluctua- 

 tions of growth in trees may be compared to the rising 

 and the falling of a wave, which attains a certain eleva- 

 tion over the ocean's surface, and then sinks into its depths 

 and disappears. 



Now, the trunk of a tree rises at first from the seed as 

 an herbaceous stem ; but, as it usually becomes more or 

 less woody before the close of the vegetative season, when 

 it enters on the stage of rest in Winter, it is not destroyed 

 by the severity of the season. Only its foliage perishes. 

 We have seen how the foliage is renewed upon fresh shoots 

 from the terminal and lateral buds of the young stem every 

 .season ; in fact, the axis with its branches is the only per- 

 manently enduring part of the tree. 



In some trees these fluctuations of growth, or vibratory, 

 movements between a state of rest and that of motion, last 

 for hundreds and even thousands of years ; but the tree, 

 like every other living organized form, is compelled at 

 last to pay back the debt due to Nature, and yields to the 

 earth and air those borrowed elements out of which it ori- 

 ginated. 



In order that the reader may form a more definite idea 

 of the nature of these waves of growth, we have ventured 

 to classify them as follows. In the life of a tree, we may 

 distinguish three principal waves of growth, or accelerated 

 and retarded vital movements. 



The Annual Wave. During winter, the trees of tempe- 

 rate climates, like the seeds in the ground, are in a state 

 of passive vitality. Life exists in both, although there is 



