:hai\ II] HEAT 49 



4. ACCLIMATIZATION. 



The absolute extremes of temperature of plant-life are constant for 

 ndividual species, but tite cardinal points vary for the separate fnnctions 

 ■ccording to climatic conditions ; they are susceptible of a limited displacc- 

 iient, either upwards or downwards, so that a plant when transferred from 

 ne climate to another with a different temperature may, provided the 

 ittcr climate is not too dissimilar, often adapt itself to its new environment 

 lid become acclimatized. The possibility of acclimatization always varies 

 ■ith the species ; in some it appears to be unlimited under natural 

 onditions, while in others it takes place only within very narrow limits. 

 ."omplete acclimatization is therefore only possible when all the cardinal 

 oints change in harmony with the new temperatures. If this is not the 

 ase, or not sufficiently so for certain functions, acclimatization is confined 



definite processes, and the plant either is not capable of existing or does 

 ot develop completely. It has already been mentioned that many 

 emperate cultivated plants exhibit vigorous vegetative growth in the 

 ropics, whereas they blossom but seldom ; in such cases, the cardinal 

 oints for the growth of flowers, and perhaps also for their inception, 

 re either not raised or not raised sufiiciently. On the other hand, many 

 lants from the warm zones do not produce flower or fruit in colder 

 ountries, because the minimum temperature necessary for their production 

 i not attained. 



A plant may be cultivated and, as observations in the polar zones and 



1 the Alps show, in cases of rich vegetative propagation, even exist in 

 le wild state, without producing seed. If, however, the cardinal points 

 )r such indispensable functions as germination, growth, nutrition, and 

 3 forth in a new climate have not been correspondingly displaced down- 

 ■ards or upwards, then the continued existence of the plant is obviously 

 npossible. 



If we compare individuals of the same species in climates of different 

 :mperatures, we soon become convinced that certain functions in hot 

 limates are associated with higher temperatures than in cold climates, 

 he cardinal points of temperature are therefore not the same everywhere, 

 'he difference is first of all hereditary, so that, for instance, seeds from 



cold climate germinate in a warmer one for some years at lower tempera- 

 -ires than do seeds of the same species that have been produced in this 

 armer zone, and the plants developing from them grow more quickly. 

 'Ut soon, however, owing to a gradual upward displacement of the cardinal 

 oints, this difference disappears. The reverse takes place when the 

 ansference is from a warmer to a colder zone. 



' In the year 1852, maize for poultry (from Hohenheiin near Stuttgart) was 

 arvested on September 22, 120 days after the sowing. . . . This maize year 



;HiMriiR Yj 



