44 METABOLISM 



vations show that the temperature of the plant is nevertheless on the whole 

 about that of the air, and that can be possible only if cooling takes place after 

 the increase in temperature due to the absorption of light rays. Heat, however, 

 is necessary for evaporation of water, and hence transpiration must be accom- 

 panied by reduction of temperature. It should be remembered in this relation 

 that we make use of this cooling effect of evaporation in everyday life when 

 we sprinkle water about during a hot summer day, or when we store water 

 in an unglazed earthenware vessel. If evaporation be thus a regulator of 

 temperature in the plant, a considerable rise in temperature must be observable 

 in feebly transpiring plants when exposed to the sun. Askenasy (1876) was 

 able to observe very high temperatures in certain oily plants, [Ursprung's 

 researches (1903, Bibliotheca botanica. Heft 60) may be compared with those 

 of Askenasy, which on the whole they confirm.] 



Temperature of plant. Temperature of air. 

 Sentpervtvum alpinum . . , 49.3° C. 



„ sp. 



Aubreiia deltoides 

 Sempervivum alpinum 



,, arenarium 



Opuntia raffinesquiana 

 Gentiana cruciata 



31.0° c. 



28.1° c. 



While plants like Auhretia and Gentiana reach a temperature very little 

 above that of the air, oily plants attain a temperature of over 50° C. This 

 observation is of special interest when taken in conjunction with the fact that 

 by far the majority of plants cannot endure so high a temperature. We see 

 also how the power of resisting high temperatures must be a characteristic of 

 such plants as are capable of living in dry climates, and that by no means all 

 plants can adapt themselves to such vital conditions. 



Bibliography to Lecture IV. 



AuBERT. 1892. Annales d. sc. nat. vii, 16. 



Askenasy. 1875. Bot. Ztg. 33, 441. 



Benecke. 1899. Bot. Ztg. 57, Abt. II, 130, Note. 



Bonnier and Mangin. 1884. Annales d. sc. nat. vi, 17, 288. 



BoussiNGAULT. 1 878. Agronomie, 6, 349. 



Brown and Escombe. 1900. Phil. Trans. R. Soc. B. 193, 223. 



BuRGERSTEiN. 1887-1901. Materialien zu einer Monographie d. Transpiration, I, 



II, III, Verh. d. zool.-bot. Gesell. Wien, 47, 691 ; 49, 399 ; 51, 49. 

 CoPELAND. 1902. Annals of Bot. 16, 327. 

 Darwin. 1898. Phil. Trans. R. Soc. B. 190, 531. 



Haberlandt. 1 896. Physiol. Pflanzenanatomie, sect. IX. 2nd ed. Leipzig. 

 Hales. 1748. Statik der Gewachse. Halle. 

 Kohl. 1886. Die Transpiration d. Pflanzen, etc. Braunschweig. 

 Leitgeb. 1896. Mitt. a. d. bot. Institut Graz, i, 123. 

 Moll. 1884. Archives neerlandaises, 18. 



Noll. 1902. Bonner Lehrbuch d. Botanik, 5th ed. p. 157. Jena. 

 ScHiMPER. 1898. Pflanzengeographie auf biolog. Grundlage. Jena. 

 Schwendener. 1881. Monatsber. Berl. Akad. p. 833 ; Ges. Abh. 1898, i, 33. 

 Stahl. 1893. Ann. Jardin Buitenzorg, 11, 98. 

 Stahl. 1894, Bot. Ztg. 52, I. Abt., 117. 

 Stahl. 1896. Ann. Jardin Buitenzorg, 13, 137. 

 Vesque. 1878. Annales d. sc. nat. vi, 6, 183. 

 VoLKENS. 1887. Flora d. agypt.-arab. Wiiste, p. 51. BerUn. 

 Wiesner. 1882. Sitzungsber. Wiener Akad. 86. 



[A very complete discussion of all the questions relating to transpiration will 

 be found in A. Burgenstein's (1904) Die Transpiration der Pflanzen ; eine physio- 

 logische Monographie. Jena.] 



