2/0 LECTURE XIII. 



The following determinations were made by Haberlandt : 



Minimum between 



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



Barley, Flax, Pea ) " 



Sunflower. Maize 4'8 io'5 



Pumpkin, Tobacco io'5 15*6 



Melon, Cucumber I5'6 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 Scgetum germinated at a temperature 

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

 a day at I3R. Wiesner ascertained that the spores of 

 Penicillium glancum 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 o C. (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 iiC. Again, the decomposition of carbon 



