50 8 Theory of the Nutrition [BOOK in. 



whole massof facts accumulated by Goeppert in his bookof 1830, 

 from which he tried to prove (p. 228) that plants at no period of 

 their life possess the power of generating heat a view which 

 he retracted however in 1832, when he had observed a rise 

 of temperature in germinating plants, bulbs, tubers, and in 

 green plants, when collected into heaps. How difficult it was 

 for physiologists under the dominion of the ' vital force ' to 

 hold firmly to the simple principle of natural heat, and not to be 

 led away by isolated observations, is shown by the expressions 

 of De Candolle in 1835, and still more by those of Treviranus 

 in 1838. It is therefore refreshing to see Meyen in his ' Neues 

 System' (1838), vol. ii, warmly asserting this principle, and 

 making the development of heat in plants a necessary con- 

 sequence of their respiration and of other chemical processes. 

 Meyen himself produced no new observations ; but Vrolik 

 and De Vriese showed by laborious experiments in 1836 and 

 1839 the dependence of the generation of heat in the flowers 

 of Aroideae on the absorption of oxygen. A higher importance 

 as regards the general principle attaches to the attempt of Du- 

 trochet in 1840 to prove that even growing shoots generate 

 small quantities of heat, as shown by a thermo-electric ap- 

 paratus. Some of the details in these observations are open 

 to objection ; but it cannot be denied that they are based on a 

 clear recognition of the general principle, though they ignore 

 the consideration that the generation of heat in plants is not 

 necessarily accompanied with a rise in temperature, since 

 cooling causes may be acting at the same time with greater 

 effect. However the doctrine of the natural heat of plants 

 was in the main established by the observations of de Saussure, 

 Vrolik, De Vriese, and Dutrochet, and by Meyen's and Du- 

 trochet's assertion of the principle laid down by Lavoisier, 

 though thirty years elapsed before it became an accepted truth 

 in vegetable physiology. 



The crude idea of a vital force was deprived of one of its 

 chief supports when it was recognised that the natural heat of 



