50 THE FACTORS [Part I 



after year ripened more and more rapidly, so that in 1857 it was harvested 90 days 

 after sowing. Seed of the same maize from Breslau, sown in the same bed and 

 at the same time as the former, took 122 days to ripen V 



Twigs of woody plants behave in the same way as seeds. A. de Candolle 

 kept twigs of Populus alba, Carpinus Betulus, Catalpa bignonioides, and 

 Liriodendron Tulipifera, some of which had grown in Montpellier and others 

 in Geneva, from February 4 onwards, in a frame, the temperature of which 

 varied between 7 and io° C. The twigs from Geneva produced leaves 

 earlier than those from Montpellier. 



By means of such observations as these the existence of a limited 

 acclimatization has been demonstrated beyond doubt. More extended 

 and exact investigations are necessary to determine the amplitude of "the 

 possible oscillations of the several cardinal points. 



In regard to the acclimatization of important forest trees in Europe, 

 North America, and Japan, H. Mayr 2 has collected information, which 

 may claim wide interest as bearing upon the general question of naturaliza- 

 tion. According to this evidence most woody species enjoy good health 

 when they are transferred to a climate slightly warmer than that of their 

 native home. He says : — 



' Broad-leaved trees easily adapt themselves to a warmer climate by prolonging 

 their whole course of development ; our native oak (Quercus pedunculata) when 

 brought from its moderately warm home into the climatically allied region of the 

 subtropical zone, for example into California, at first grows very fast, and in the 

 similar climatic zone of Australia attains a height of 7 meters in nine years. Japanese 

 oaks (Quercus glandulifera and serrata) used for charcoal-making are extensively 

 grown as coppice in the subtropical area of Japan, where in eight years they 

 become as tall as in fifteen years in their own home. Paulownia imperialis, rare 

 specimens of which grow well in the warm deciduous mountain forests of Japan, 

 is cultivated for the sake of its wood in the subtropical region, where in virtue of its 

 extraordinarily rapid growth it produces a very light wood, which neither warps nor 

 shrinks. The tree repays cultivation better in the latter place than in its own home, 

 but it is already exhausted after twenty years, becomes hollow and dies, whereas in 

 its home, until recently, trees 6-7 meters in girth and 48 meters up to the crown 

 were not rare. 



' In the same way, plants transferred from subtropical zones into the tropics 

 exhibit an increased power of growth in the first decades. The Japanese camphor- 

 tree, for instance, belongs to the subtropical zone of evergreens ; in the tropics 

 of India and Java it grows remarkably fast ; its vigour of growth causes the stem 

 to divide into innumerable strong branches, so that the tree loses its ancestral form. 

 It is very probable that, owing to this accelerated growth during youth, an earlier 

 consumption of vitality and an earlier natural death is brought about: for remark- 

 ably early and excessive production of seed characterizes all kinds of woody species 



1 Schuebeler, op. cit., p. 80. Many cases of expedited or delayed development are given 

 by H. Hoffmann. 2 H. Mayr, op. cit., pp. 365-368. 



