CHEMICAL PHENOMENA IN LIFE 



leaves which were kept in a chest carefully isolated 

 to prevent loss of warmth. We may consider that 

 heat is generally produced by plants, just in the 

 same way as by warm-blooded vertebrates. But 

 there are no contrivances in plants to keep the 

 temperature at a certain point above the tempera- 

 ture level of their surroundings. From numerous 

 experiments we learn that plants are in their vital 

 functions adapted to a certain average tempera- 

 ture. Not a few tropical plants suffer from frost 

 and even die when the outside temperature falls 

 below four degrees above zero. At the same 

 temperature, on the other hand, many alpine 

 and arctic plants have to perform all their functions 

 in life. In tropical plants the fat of the seeds melts 

 as a rule at a temperature of 30 to 40 degrees. It is 

 solid at the ordinary room temperature of 15 

 degrees. European plants always show the melting- 

 point of their fat not far above zero. Daily 

 observation teaches us that plant life develops 

 considerably more quickly in a higher temperature. 

 Growth, respiration, and the assimilation of carbon 

 dioxide, as well as the phenomena of movement 

 and stimulation, reach a much higher velocity 

 and power in a temperature of 30 to 35 degrees 

 than in one below 20, and by far higher than in a 

 temperature below 10 degrees. 



The eminent Dutch chemist Jacobus Hendricus 

 Van 't Hoff discovered the rule that chemical 

 reactions are influenced by temperature with the 

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