34 



Lepidium and Linum did not germinate at 0° C, but did germinate 

 •at 1.8° C. 



CoUomia did not germinate at 3° C but did germinate at 5.3° C. 



Xigella^ Iheris, and Trifolhim repens did not germinate at 5.3° C.. 

 but did germinate at 5.7° C. 



Mays did not germinate at 5.7° C, but did germinate at 9° C. 



Semmum did not germinate at 9° C, but did germinate at 13° C. 



Melon did not germinate at 13° C.. but did germinate at 17° C. 



Malvaceae, Gossypium lierhaceum ; variety not specified: Some cot- 

 ton seeds on which experiments had been made two years before 

 would not then germinate, but did germinate at this time at 40° C. 



Raphanus sativus (radish) : Lefebure had shown that these seeds 

 germinate at 5° or 6° C. as their minimum temperature. 



Trltkum (winfer wheat), Hordeum (barley), Secede cereale (rye) : 

 All of these Graminese germinated at 7° C, according to Edwards 

 and Colin, but this is probably not their minimum, for certainly 

 barley will germinate at a lower temperature by prolonging the 

 experiments. i 



We conclude, therefore, that each species has a minimum tempera- 

 ture at which it germinates, and the ordinary experience of the farmer 

 would suggest this, but in his work one can hardly decide whether 

 seeds sown too early in the springtime are simply retarded by specific 

 low temperatures or Avhether germination is quite impossible. These 

 present experiments show that if the temperature is too low, then 

 germination is prevented. In calculations on the relation of temper- 

 ature to vegetation, one must consider only facts deduced from pro- 

 longed, constant temperatures. In the stud}' of growth under natural 

 conditions one must consider certain temperatures as useless and 

 ineffective as concerns the germination of certain species of plants. 

 There are, moreoA^er, other facts that show that the same rule holds 

 good for leafing, flowering, and maturing. 



According to De Candolle's experim.ents, the species that require 

 high temjDeratures as minima for germination are all from warm 

 countries. Such species can not flourish in cold countries, for if they 

 do germinate there this happens too late in the springtime and they 

 can not ripen their fruits before winter. Among the species which 

 germinate at low temperatures there are some that can exist in tem- 

 perate climates, but these do not extend very far toward polar regions, 

 either for reasons foreign to the germination or else because, having 

 germinated too early, the delicate shoots are killed by frost. 



(3) There is for each seed a maximum temperature beyond which 

 germination is impossible. The above experiments determine such 

 maxima approximately as follows : 



Nigella does not germinate if the mean temperature exceeds 28° C. 

 CoUomia does not germinate if the mean temperature exceeds 28° C. 



