(J5 



During the 1"^ and 2"^' da^s the loss of energy per hour per kilogram of 



1000 



ihe initial-weight was therefore roughly X '^ =83 cal. 



48 



1000 

 The same for the 3'^^ day X 34 = 1417 „ 



>j 5> >> j> 4 ' ,, ,, X ^4 = 225U ,, 



„ ,, ,, ,, 5 ' ,, ,, X "'^ =^ oooo ,, 



„ „ „ „ 6t'' „ „ X Ö6 = 4000 „ 



„ „ „ „ 7^" „ „ X180= 7500 „ 



This amount of lost eliemieal energy corresponds Iherefore in all 

 probability to that which is ap[)lied to osmotic purposes, to the over- 

 coming of resistances and lo the evolution of heat. 



In a second series of observations I also attempted to determine 

 directly the anmunt of heat that is given off. The principle, that 

 underlay these determinations, was briefly as follows : air, satui-ated 

 with water-vapour, which had been brought to a constant known 

 temperature, was passed over germinating wheat-grains at a constant 

 velocity; these acted as a continuous source of heat; the air which 

 passed ovei"» it therefore rose in temperature. 



If the difference of temperature l)etween the air streaming in and 

 out vvei'e measured, when the latter passed at a known rate, then 

 in the ideal case when absolutely no other heat conduction took 

 place, the amount of heat set free could be calculated from «the 

 known heat-capacity of the air. Moreover for this the space in which 

 the seedlings were placed would have to be completely saturated with 

 water- vapour ; if this were not so, evaporation would take place on 

 germination, in which wnj heat would be withdrawn from the 

 observation. 



The apparatus with which I conducted these experiments consisted 

 of a copper vessel placed in a waterbath of constant temperature. 

 Through this copper vessel, in which a large number of germinating 

 wheat-grains were placed, a current of air was directed at the rate 

 of 3 litres per hour; the air had had for a large part of its course an 

 opportunity to take up the constant temperature of the water. A set 

 of thermal needles served to measure the difference between the tem- 

 peratures of the air entering and leaving ; the current resulting 

 from this difference in temperature was led through a very sensitive 

 mirror-galvanometer, whilst a spot of light was thiovvn by the mirror 

 on a scale and so made it possible to compare accurately the deflections. 



The apparatus was for the most part composed of materials which 



5 



Troceedings Royal Acad. Amsterdam. Vol. XVII. 



