330 Prof. De Candolle (yti the Longevity of Trees^ 



noted, by comparing the computed with the observed altitude, 

 to determine the amount of refraction at each observation. 



When the latitude of the place is once known, the N. P. D.'s 

 of all the stars which pass between the pole and the zenith can 

 readily be found, by observing their greatest east and west azi- 

 muths. Observations, then, on their greatest and least altitudes 

 will readily give the refractions, but when the latitude is much 

 above 45°, this method will not enable us to determine refrac- 

 tions near the horizon. A judicious selection of pairs of obser- 

 vations will enable the astronomer, in a single day, to obtain 

 correctly the latitude of his observatory ; and he will thus avoid 

 the trouble of applying the corrections for nutation and aberra- 

 tion, which would become necessary if the period of his experi- 

 ment were much extended. 



\2th August 1833. 



ON THE LONGEVITY OF TREES AND THE MEANS OE ASCERTAIN- 



iNG IT. By Professor De Candolle, 



A TREE may be considered in two points of view ; it may 

 either be said to be a collection of as many individuals united as 

 are developed by buds on its surface, or as a simple individual, 

 analogous to what is so called in speaking of animals. In the 

 first mode of expression, probably the most rational, we cannot 

 be surprised, that new buds being constantly added to the old 

 ones, the aggregate which results from it has no necessar}^ limit 

 to its existence. In the second, which is the more common, it 

 must be admitted, that as a new woody layer is formed every 

 year, and generally new organs in the greater number of trees, 

 in vegetables this gradually increasing hardness (ossification) and 

 obstipation in old and permanent organs ought not to occur, in 

 which death from decrepitude, properly speaking, consists, and 

 that of course trees should not die unless from accidental causes. 

 By either of these hypotheses we arrive at the inference, that 

 trees do not die of old age in the real sense of the word, smd 

 that, in consequence, we might find some which have attained 

 an extraordinary age. 



It is not enough, however, to conceive this opinion, we must 

 endeavour to establish it. Two remarkable instances have been 



