226 THE POWER OF RESISTANCE TO EXTREMES 



exposure to a temperature of from 45 to 46 C. kills most Phanerogams, and 

 a still lower temperature must ultimately cause the death of all those 

 autotrophic plants in which photosynthesis becomes less active than 

 respiration at temperatures of 37 to 39 C. 1 After short exposure to 

 fatally high temperatures plants often appear at first fresh and living, 

 but die as an after-effect of the exposure even under the best external 

 conditions 2 . 



The best' instance of the different resistances at various stages of 

 development is afforded by bacteria, for in many cases the spores are 

 not killed by boiling for from thirty minutes to several hours, without 

 the organisms being especially resistant in the vegetative condition, 

 although in the case of thermophile forms both stages are unusually resistant 

 to high temperatures. The spores of Bacillus snbtilis, for instance, can stand 

 half an hour's boiling, although the maximum temperature for growth lies 

 at 50 C., and although in the vegetative condition death soon ensues 



at 55 C. 3 



The degree of maturity and the cultural conditions seem to influence 

 the resistant powers of spores, which naturally also differ according to the 

 organism which forms the spores. All degrees of resistance are in fact 

 shown, from spores which withstand several hours' boiling, to those of 

 Bacillus antJiracis, which are killed in two minutes, and to those which 

 cannot stand boiling at all 4 . The spores of fungi and of yeast are 

 also more resistant than the vegetative cells, although they are readily 

 killed by temperatures lying well beneath iooC. 5 The fact that 

 certain seeds when moist are hardly more resistant than the seedlings 

 they produce 6 shows that the power of resisting moist heat is not connected 

 with the accumulation of reserve materials, or with the power of with- 

 standing desiccation. The same applies to mosses and lichens, for 

 Bryum caespiticinm and Cladonia rangiferina when moist are killed 

 by less than a day's exposure to 45 C., although they can withstand 

 severe desiccation, and in this condition require six hours' exposure to 

 90 C., or a day's exposure to 70 C., to kill them 7 . That the passage 

 into a resting condition does not always involve an increased resistance 

 to heat is shown by the readiness with which- winter buds and resting 

 cambium are killed by high temperatures. 



No organism, whether in the spore condition or not. is able to withstand 

 prolonged boiling, and if the water is heated under pressure to from no 



1 Ewart, Journ. of Linn. Soc., 1896, p. 385. 2 Cf. Sachs, Flora, 1864, p. 24. 



3 Cohn, Beitr. z. Biol. d. Pflanzen, 1877, Bd. n, p. 271. On Bacillus carotarum see Koch, Bot. 

 Ztg., 1888, p. 297. 



4 Cf. Fliigge, Die Mikroorganismen, 1896, 3. Aufl., Bd. I, p. 438. 



5 Cf. Jorgensen, Mikroorganismen der Gahrungsindustrie, 1898, 4. Aufl., p. 180; Kayser, Ann. 

 d. 1'Inst. Pasteur, 1889, T. in, p. 513. 



6 Just, Cohn's Beitr. z. Biol., 1877, Bd. II, p. 346. 7 Ewart, 1. c., pp. 369, 376, 388. 



