BY P. OLSSON-SEFFER, PH. D. Ill 



individuals of the same species just like any other physiological 

 or morphological peculiarity, it becomes possible to acclimatize 

 a tender plant by propagating hardy varieties. 



We have already mentioned the lowest temperature at which 

 perceptible growth takes place, but this minimum does not 

 necessarily suffice for the developement of chlorophyll, or for 

 assimilation, or for the irritability of motile organs and so 

 forth ; and when this is determined for one species of plant, the 

 lower zero points of these functions in another species are by no 

 means necessarily the same. The diversity of the lower zero- 

 points of the various functions may however bring it about 

 that at certain lower temperatures the various functions no 

 longer work harmoniously together, so that pathological con- 

 ditions are induced. It is observed in northern countries that 

 the young leaves of cereal plants grow in the early spring, but in 

 spite of bright illumination they remain yellow, because the 

 lower limit of temperature for growth is not so high as that for 

 the development of chlorophyll. 



Not only the low temperature but also the length of its 

 duration will be decisive for the destiny of the plant. We have 

 no exact observations as to the length of time during which the 

 vitality of a frozen plant persists. It is stated that after the 

 recession of a glacier in Chamouni several plants which had 

 been covered by ice for at least four years resumed their growth. 



If the rays of the sun immediately after its rising reach the 

 frozen plant, the ice will not only melt but also evaporate, 

 consuming a great quantity of heat. The greatest part of this 

 heat naturally comes fiom the sun, but one part is still derived 

 from the little store of the plant, and it is probable that the 

 last determining cause of the damage done by a night frost often 

 depends on this circumstance. It would be wrong to believe 

 that whenever rime round the plants is produced, the sunrise 

 being clear, damage by frost will instantly occur. Lemstrom 

 has shown that plants possess a certain power of resistance 

 against frost, and that they are not in general destroyed if they 

 are covered with ice at a temperature of — 2" C. near the ground 

 by clear sunrise, the time of the duration of the low temperature 

 not exceeding 1^ hours. Kihlman and others have come to 

 the same conclusion. 



