236 



THE RATE OF GROWTH 



[CH. 



and Acacia; the deciduous trees included Quercus, Populus, Robinia 

 and Melia. The result (Fig. 70) is much as we might expect. 

 The deciduous trees cease to grow in winter-time, and during 

 all the months when the trees are bare; during the warm season 

 the monthly values are regularly graded, approximately in a sine- 

 curve, with a clear maximum (in the southern hemisphere) about 

 the month of December. In the evergreens the amplitude of the 



Fig. 70. Periodic annual fluctuation in rate of growth of trees in 

 the southern hemisphere. From C. E. Hall's data. 



annual wave is much less ; there is a notable amount of growth all 

 the year round, and while there is a marked diminution in rate 

 during the coldest months, there is a tendency towards equality 

 over a considerable part of the warmer season. In short, the 

 evergreens, at least in this case, do not grow the faster as the 

 temperature continues to rise; and it seems probable that some of 

 them, especially the pines, are definitely retarded in their growth, 

 either by a temperature above their optimum or by a deficiency of 

 moisture, during the hottest season of the year. 



Fig. 71 shews how a cypress never ceased to grow, but had alternate 



