Chap. II] HEAT 5 x 



that are placed in such circumstances. If in introducing a woody species a zone of 

 vegetation is entirely passed over, as when deciduous broad-leaved trees are brought 

 into the tropics, they grow so feebly, according to experience derived from India 

 and Java, that we must describe them as incapable of cultivation '.' 



According to Mayr, ' Conifers appear to adapt themselves to a new climate with 

 more difficulty than broad-leaved trees. Thus the conifers of the cool area, firs, 

 spruces and larches, whether European or Japanese, are so arrested in growth in 

 the subtropical area, becoming bush-headed and branchy, that they can hardly 

 be considered capable of cultivation there. 



' The transference from a warmer to a cooler zone usually yields unfavourable 

 results: all woody species when brought from their home— by which is meant area 

 of distribution— into a cooler area, lose their importance as cultivated plants, at any 

 rate from a sylvicultural point of view, owing to injuries of all kinds, absence 

 or rarity of ripe fruits, production of wood of little value, and so on. 



' In the warm subtropical coasts of South California all kinds of palms and trees 

 from the tropical area may be cultivated, but only for ornamental purposes, as they 

 mature no fruits. . . . 



' In this transference to a cooler climate some remarkable phenomena are often 

 encountered ; woody species become sensitive to frost, a condition not to be 

 expected, judging from their native habitat ; others prove to be hardy in relation to 

 frost, though, in their home, they could not have occasion to defend themselves 

 against it. 



' It is well known that plants are much less susceptible to frost during their 

 winter rest than during the vegetative season in spring and autumn ; we see from 

 their behaviour in relation to late and early frosts how difficult it is for a plant 

 to adapt itself to a colder climate ; many species seem to find it quite impossible 

 either to delay the commencement of their development or to hasten its termination, 

 in other words to become frost-hardy. Gleditschia and Robinia are natives of the 

 southern Atlantic States of North America, an area where, as regards summer and 

 winter temperature, the duration of the vegetative period exceeds that of our 

 warmest vine-countries ; both trees are cultivated in America, Europe, and Asia far 

 beyond their region of distribution ; but during the long period of their cultivation 

 not a single race has been produced that is secured against the frost by a shortening 

 of its vegetative season ; moreover, it is well known that the seed of the Robinia 

 is always taken from trees that have already grown in a cold climate ; the seedlings 

 retain the peculiarities of the mother-tree unchanged.' 



1 See also in this book, Part III, Sect. I, Chap. II, Periodic Phenomena in the 

 Tropics. 



E 2 



