Jan. 1898.] BOTANICAL SOCIETY OF EDINBUKGH 97 



secure a large number of trees from the same neighbour- 

 hood, and of approximately the same age, so as to compare 

 their curves of increment. 



While considering the external influences of a plant, one 

 must not overlook the internal conditions. Perennial 

 plants store up the surplus food of one year to be used 

 during the following year, but the balance carried over 

 from one year to another depends largely on the conditions 

 of growth ; consequently the growth of any one year is not 

 wholly dependent on the meteorological conditions of that 

 year, but also on the reserved food materials, which, in 

 turn, are dependent on the meteorological conditions of the 

 preceding year. 



Again, insect attacks and severe frosts may so injure the 

 buds and leaves of trees during the growing season as to 

 make their effects felt over a period of years. 



These are some of the difficulties to be met with in 

 trying to account for the rise and fall of the increment 

 curve. 



Sylvicultural methods have never been adopted where 

 those trees grew. I am assured of this by Mr. John 

 Michie, head forester, Balmoral ; the trees were planted 

 and left to nature, consequently thinnings need not be 

 considered. Gales of wind may have levelled trees around 

 the specimens now under consideration ; but, although 

 Mr. Aitken in his reports notes the occurrence of gales, 

 he mentions only that of November 1893 as having been 

 destructive to trees. 



If the curve of larch A be examined, it will be seen 

 to contain six well-marked maxima in 1859, '70, '75, '82, 

 '89, and '93 respectively, as well as a few other maxima of 

 less importance; and three deep minima in 1864, '79, and 

 '92 respectively, and several other depressions. To under- 

 stand these points it must be remembered that larch thrives 

 best in a dry, sunny atmosphere. 



The maxima of 1859, '70, '75, and '82 occurred when 

 the amount of sunshine for the growing season was above 

 the mean. The minima of 1879 and 1892 occurred when 

 the sunshine was very much below the mean. The 

 minimum of 1864 occurred during one of the maximum 

 sunshine periods, and, as this occurrence seems to contradict 



TRANS. EOT. SOC. EDIN. VOL. XXI. H 



