PROGRESS OF VEGETATION. 325 



have attained their full size and are in complete 

 action, sap appears in the bark as well as the 

 wood. The sap which then appears is not how- 

 ever the same as that which was in the wood 

 before the leaves came on. The air, heat, and 

 light have all had an influence upon it in the 

 leaves, and fitted it for the composition of the new 

 substance. 



In the young shoots, those that have been pre- 

 pared the same season, the process is the same as 

 it was in the first oak, but in the other parts, the 

 prepared juice spreads itself between the wood 

 and the bark. First in a state nearly fluid, but 

 it gradually becomes a little granular, then fibrous, 

 and it ultimately divides into wood and bark in 

 the same manner as that of the former year ; and 

 when that has been completely performed, the 

 leaves are " healed off, " and the tree passes into 

 its repose as before. The result of the annual 

 action has been to case the former tree, roots, and 

 all, with a new layer of wood and bark, and to 

 lengthen it by a twig at every bud. If we could 

 by any means separate the two trees by pulling 

 the first out of the second, as an instrument is 

 pulled out of its case, we should have a sight of 

 two years' progress of the oak, and only the leaves 

 would be wanting to give us the whole of what 

 had grown from the acorn during those years. 

 The third and every succeeding year is merely a 

 repetition of what took place during the second, 

 only the action of each year is on a larger scale 

 than that of the preceding year ; and the addi- 

 tions become gradually greater and greater till 

 about the middle period of the tree's duration, and 

 then they gradually become less and less every year 

 p f 



