540 ORGANOLOGY. 



rise and fall ; if these conditions are of long duration, the tempera- 

 ture of the tree continually approximates more and more towards 

 them, without, however, entirely reaching their degree of intensity. 

 The reason of this phenomenon may, in all probability, be attri- 

 buted to the temperature of the earth at the depths to which the 

 roots extend ; the temperature is thence imparted to the stem, 

 partly by means of the rising sap, and partly also through the great 

 capacity of conducting heat possessed by the wood in its longi- 

 tudinal direction; and it is protected and preserved in the stem, 

 partly owing to the inferior conducting power possessed by the 

 wood in its transverse direction, and partly also owing to the bark, 

 which is itself a very bad conductor of heat. 



C. The Aracece (in which the effect is more readily traceable, 

 owing to the number of flowers aggregated together) develope, 

 during their period of flowering, a temperature far exceeding that 

 of the surrounding atmosphere. The reason of this is also to be 

 attributed to the formation of carbonic acid (a process of combus- 

 tion), which is especially maintained by the stamens. 



Respecting the subjects touched upon in this and the following para- 

 graphs of the general Organology, I must confine myself to reference to 

 the labours of others, indicating the problems that are still to be solved, 

 as I have not yet been enabled to institute observations of my own. 



Every one who knows any thing of malting for the purposes of 

 brewing must be acquainted with the rise of temperature that takes 

 place during the germinating process of the plants. This fact is beyond 

 dispute ; but I am not aware of any scientific observations on the subject. 

 They ought to be instituted in such a manner as to embrace the entire 

 act of germination up to the cessation of the formation of carbonic acid ; 

 during this period the entire quantity of carbonic acid, as well as the 

 quantity formed during the individual periods, ought also to be ascer- 

 tained ; the quantity of water formed ought also to be calculated accord- 

 ing to the well-known composition of the starch, and the temperature gene- 

 rated from both through the chemical changes should be determined, arid 

 be compared with the temperature observed. 



Observations respecting the temperature of trees were first insti- 

 tuted by John Hunter, subsequently repeated by many with different 

 results ; and animated controversies were carried on upon the subject, of 

 which Meyen* gives an elaborate account. 



All former investigations, however, appear to me to be superfluous 

 after the observations of Schliblerf, the first that were accurate and insti- 

 tuted in a scientific spirit. These researches resulted in the law enun- 

 ciated in the text. The derivation of it from the temperature of the 

 earth is still hypothetical, and accurate observations on certain plants, 

 with simultaneous observations on the temperature of the earth at about 

 the depth of the roots, are much to be desired. It becomes however very 

 probable, after the known facts of the course of the temperature, of the 



* Physiologic, vol. ii. p. 164. 



f Haider, Beobachtungen iiber die Temperatur der Vegctabilien, Tiibingen, 1826; 



and Neuffer, Untersuchungen iiber die Temperaturver nderungen der Vegetabilien, 



&c. Tiibingen. 1829. 



