2/O LECTURE XIII. 



The following determinations were made by Haberlandt : 



Minimum between 



Buckwheat, Hemp, Oat, Rye, Rape, Wheat,") 



Barley, Flax, Pea j ~~ 4'8 C. 



Sunflower, Maize 4-8 10*5 ,, 



Pumpkin, Tobacco 10-5 15*6 



Melon, Cucumber 15-6 18*5 



Hoffmann observed that the spores of many Fungi do 

 not germinate when the temperature is near the freezing- 

 point, and that those which do germinate do so very slowly : 

 thus, spores of Uredo Segetum germinated at a temperature 

 of 0*4 O'8 R. in six days, whereas they germinated in half 

 a day at I3R. Wiesner ascertained that the spores of 

 Penicillium glaucum can germinate at 1*5 C., but that germi- 

 nation at that temperature is not followed by the develop- 

 ment of a mycelium. 



The effect of a low temperature upon individual metabolic 

 processes is also well marked. It is well known, for instance, 

 that the unorganised ferments are only active at a tempera- 

 ture considerably above oC. (Schiitzenberger). With regard 

 to respiration it has been already pointed out (p. 198) that 

 the absorption of oxygen and the evolution of carbon dioxide 

 is less considerable at a low than at a relatively high tempera- 

 ture, and that the former process goes on more actively at 

 low temperature than does the latter ; it appears that the 

 zero-point for the absorption of oxygen is lower than that 

 for the evolution of carbon dioxide. The actual zero-points 

 for these processes have not been determined, but they are 

 undoubtedly lower than that for growth in the case of any 

 given plant. It was mentioned in a previous lecture (p. 239) 

 that when normally green plants are exposed to a low 

 temperature the newly-formed organs are yellow, that is, 

 that chlorophyll is not formed in them. Sachs has deter- 

 mined the lowest temperature at which the chlorophyll- 

 corpuscles turn green in the following plants : in Phaseolus 

 multiflorus, in Zea Mais, in Sinapis alba, and in Brassica 

 Napus at above 6 C. ; in Pinus Pinea and canadensis be- 

 tween 7 and nC. Again, the decomposition of carbon 



