Ill 



OF THE GROWTH OF TREES 



237 



spells of quicker and slower growth, according to conditions of 

 which we are not informed. Another figure (Fig. 72) illustrates the 

 growth in three successive seasons of the Calif ornian redwood, a near 

 ally of the most gigantic of trees. Evergreen though the redwood 

 is, its growth has periods of abeyance; there is a second minimum 

 about midsummer, and the chief maximum of the year may be that 

 before or after this. 



Fig. 71. Growth of cypress (C. macrocarpa), shewing seasonal periodicity. 

 From MacDougal's data: smoothed curve. 



1931 1932 1933 



Fig. 72. Fortnightly increase of girth in Californian redwood (Sequoia 

 sempervirens), shewing seasonal periodicity. After MacDougal. 



In warm countries tree-growth is apt to shew a double maximum, 

 for the cold of winter and the drought of summer are equally 

 antagonistic tQ it. Trees grow slower — and grow fewer — the farther 

 north we go, till only a few birches and willows remain, -stunted and 

 old; it is nearly a hundred years ago since Auguste Bravais* 

 shewed a steadily decreasing growth-rate in the forests between 

 50° and 70° N. 



* Recherches sur la croissance du pin silvestre dans le nord de I'Europe, Mdm. 

 couronnees de VAcad. R. de Belgique, xv, 64 pp., 1840-41. 



