ON THE AGE OF TREES 



In perennial plants, the tissues 

 wiiich resist climatal change carrj'^ on 

 a kind of low vitality, as seen in the 

 trunks of trees, in this country, in the 

 winter. At more favorable periods, 

 these tissues begin to grow in certain 

 directions; buds, and leaves, and new 

 tissues are formed, and deposited, in 

 various parts of the plant, more espe- 

 cially covering the old, and growth or 

 increase is the consequence. Even in 

 plants not producing leaves, this pro- 

 cess goes on, and, year after year, new 

 tissues are added to the old. This is 

 especially evident in sea-weeds, which 

 thus exist through very long periods 

 of time. Thus, Professor Schleiden 

 says, " On the great fucus bank of 

 Corvo and Flores, we might yet find, 

 floating about, plants of Sargassum, 

 which had been cut in strips by the 

 bark of Columbus ; and in the north- 

 ern drift, we might expect to discover 

 Lichens that had been transported with 

 the soil in which they grew, from 

 Scandinavia." Nor is this conjecture 

 at all unreasonable, from what we 

 know of the nature of the process of 

 growth in these plants; but we have 

 no means, in cryptogamic plants, of 

 accurately ascertaining the length of 

 time they have been in growing. Nor 

 is this possible in endogenous plants, 

 or even in all exogens; but, in the lat- 

 ter, the stem presents, very generally, 

 a series of zones, and each zone has 

 been found to correspond with one pe- 

 riod of vegetation. This period most- 

 ly represents a year, hence, by count- 

 ing the number of zones in the trunk ,( 

 of an exogenous tree, we may form an 

 estimate of the years it has existed. It 

 is in this way that the ages of many 

 very old trees have been arrived at. 

 The following list of old trees has been 

 published by Moquin-Tandon, in his 



ratologie Vegetals,hnd is reproduced 



Agave American — Endogen. 



Sections of a Stem as it appears in May and June of 

 THE Fifth Yeak. The while spaces show ilie swelling cam- 



II I 



Section* of a .''tem at the end of the Fifth Year. 

 The eii\ eiopes and la) ers of liber are too thin to be shown by 

 the pencil. 



English translation of Schleiden's Principles of Scientific Botany. There areknown. 



