222 



PHYSIOLOGY OF NUTRITION 



Bonnier 1 has carried out extensive researches upon the production of heat 

 during seed germination, using either a calorimeter of the Berthelot type or 

 the modified thermo-calorimeter of Regnault. The latter apparatus (Fig. 93) 

 consists essentially of a mercury thermometer the bulb of which is expanded to 

 form the wall of a chamber (A), the latter being closed by a stopper (B). The 

 plants or plant parts to be studied are placed in this chamber and their tem- 

 perature is directly read on the thermometer scale. In some of Bonnier's ex- 

 periments analyses of the gas contained in the chamber were also carried out. 



Pea seeds placed in this calorimeter and allowed to grow until the cotyledons 

 had disappeared produced the following amounts of heat per minute, per kilo- 

 gram of seeds, at different stages of their development. 



Heat Produced 

 Stage of Development, Pea per Minute, 



gram-calories 



1 . Soaked seeds 9 



2. Seedlings with roots 5 mm. long 125 



3. Seedlings with roots 50-60 mm. long 75 



4. Seedlings with green stem about 20 mm. long 60 



5. Seedlings with cotyledons withering 22 



6. Seedlings from which cotyledons have fallen 6 



This experiment shows that the rate of heat production varies with the develop- 

 ment of the plant, the maximum rate occurring with a very early stage of 

 germination. 



If the rates of heat liberation for the different developmental stages are cal- 

 culated from the rates of the elimination of carbon dioxide and of the absorption 

 of oxygen, the results do not agree with the corresponding ones determined 

 calorimetrically, as is clear from the following table, which gives the rates of 

 heat production per kilogram of barley seeds per minute. 



The amounts of heat actually produced in germination markedly exceed the 

 corresponding calculated amounts, and it is therefore evident that exothermic 

 reactions other than that of oxidation occur during germination, especially in 

 the earlier stages. Among such reactions are to be included starch inversion 



1 Bonnier, Gaston, Recherches sur la chaleur vegetale. Ann. sci. nat. Bot. VII, 18: 1-35- 1893. 



