SUPRA-MAXIMAL TEMPERATURES 229 



and Brefeld, on the contrary, observed no such increased resistance in 

 alkaline solutions. 



In the case of organisms which can withstand desiccation, the power 

 of resistance to heat is greatly increased by complete drying. Thus many 

 thoroughly dried seeds, mosses, lichens, fungus spores, and bacteria are 

 not killed by exposure to temperatures of 100 to as much as no or even 

 I20C. for one or more hours. The presence of a very small amount 

 of water considerably lowers the resistance, so that air-dried seeds are soon 

 killed at 100 C., or even at 60 to 80 C., if they have been previously kept 

 in moist air for some time. In many experiments no precautions were 

 taken to ensure perfect dryness, so .that the deaths observed at temperatures 

 of 60 C. may have been due to the presence of water 1 . There may of 

 course be plants which, even when perfectly dry, are soon killed by 

 temperatures at all approaching iooC. Indeed in all cases the vitality 

 of desiccated plants is ultimately lost, and at high temperatures more 

 rapidly than at normal ones. Especially good instances of graduated 

 resistance are afforded by mosses and lichens 2 . Furthermore, many plants 

 killed at 40 to 50 C. when turgid are highly resistant when dried 3 . 



The resistance of dried plants to heat was first established by Spallanzani 4 , 

 and subsequently confirmed by various investigators in the case of seeds 5 , mosses 

 and lichens 6 , fungus spores 7 , yeast-cells 8 , and bacteria 8 . Krasan, Just, and 

 Hohnel worked with completely dried seeds and found that many oily and 

 starchy seeds could withstand long heating to noC., or short exposure to 

 i2oC. The first indication of commencing injury is shown by the delay in 

 germination. Since the resistant spores of certain bacteria can withstand a 

 temperature of i3oC. for a few hours, and one of i4oC. for a short time, rapid 

 perfect sterilization can only be assured in the case of dry objects by heating to 

 temperatures of from 150 to i7oC. 



1 As regards animals cf. Artari, Abhandl. der naturf. Ges. in Halle, Bd. xxxi, p. 120. 



2 Thus, using desiccated plants, and with an exposure of six hours, Grimmia conferta and 

 Orthotrichum affine were only killed at 95 C., Ceratodon purptireum and Bryum caespiticium 

 at 90 C., Barbula mtiralis at 85 C., and Dicranum scoparium at 80 C. Cf. Ewart, Journ. 

 Linn. Soc., Vol. xxxi, 1896, p. 369. 



3 For instances cf. Ewart, 1. c., pp. 369, 374, 378, 388. 



4 Opuscules d. physique animale et ve'ge'tale, translated by Senebier, 1777, T. I, pp. 58, 62. 



' See Nobbe, Samenkunde, 1876, p. 227; v. Hohnel, Wiss.-pract. Unters. a. d. Gebiete d. 

 Pflanzenlaubes, 1877, II, p. 77; Just, Cohn's Beitr. z. Biol., 1877, Bd. n, p. 311, and the 

 literature there quoted. Rittinghaus (Verb. d. naturh. Vereins d. Rheinlande, Jahrg. XLIII, 5. 

 Folge, Bd. ill) states that pollen-grains are in part killed by heating to iooC. for fifteen minutes. 

 See also Konno, Bot. Jahresb., 1898, i. Abth., p. 609. 



* Ewart, 1. c., pp. 369-88. 



7 For the literature see de Bary, Morphol. u. Biologic d. Pilze, 1884, p. 372. 



8 Manassein, Wiesner's mikros. Untersuchungen, 1872, p. 122; Artari, 1. c. ; Kayser, Ann. d. 

 1'Inst. Pasteur, 1889, T. m, p. 520. 



Pasteur, Ann. d. chim. et d. physique, 1862, 3 s r ., T. LXIV, p. 90; Nageli, Die niederen 

 Pilze, 1877, p. 202. See also the literature given by Fliigge, Mikroorganismen, 1896, 3. Aufl., 

 Bd. I, p. 437. 



