230 THE POWER OF RESISTANCE TO EXTREMES 



The causes which determine the varying resistances of different plants 

 to heat are quite unknown. The fact that a temperature of from 20 to 40 C. 

 kills certain plants shows that in this case death is not the result of the 

 coagulation of the plant albumin. Further, some plants grow at 75 C, 

 i. e. above the temperature at which egg-albumin coagulates. Coagu- 

 lation need not always occur, for we must remember that the acid and 

 alkali albumins are not coagulated by heat, and that the presence of 

 silver 1 , iron 2 , or various organic substances 3 may retard coagulation. 

 Hence it is not surprising that the spores of many bacteria are only killed 

 by prolonged boiling. Since spores taken fresh from a culture solution, 

 and therefore saturated with water, are equally resistant, this special power 

 is not the result of desiccation, as Cohn 4 and certain other authors have 

 supposed 5 . Perfect desiccation not only decreases or inhibits many chemical 

 reactions, but also renders the seed incapable of any vital response G . The 

 presence of very little water considerably reduces the resistance of a dry 

 seed to heat, and hence the accumulation of soluble reserve materials in 

 a turgid cell is unable to produce a sufficient decrease in the percentage 

 of water to influence the power of resistance to heat. 



The observations upon the growth of organisms in very hot springs need to 

 be accepted with some caution, since it is not certain that the plant was actually 

 at the temperature given by immersing a thermometer in the surrounding water. 

 Neither transpiration nor the existence of protective sheaths are of any avail in 

 the case of submerged microscopic organisms, although in large plants partly 

 exposed to air both factors may aid in keeping down the internal temperature 

 of the plant. It is not certain whether roots develop abundantly in those layers 

 of tropical soils which may acquire a temperature of from 60 to 75 C. during the 

 day, and if they do, whether the roots have a high specific resistance, or avoid 

 injury by special means 7 . The roots of our indigenous cereals die in a few days 

 if the temperature of the soil is kept at 50 C. 8 , but other plants may behave 



1 Van der Does, Zeitsch. f. physiol. Chem., 1897, Ed. xxiv, p. 351. 



2 Clautriau, La digestion d. 1. urnes de Nepenthes, 1900, p. 25 (repr. from Me"m. couronne's, 

 etc., publics p. 1'Acad. royale de Belgique, 1900). 



3 Spiro, Zeitschr. f. physiol. Chem., 1900, Bd. xxx, p. 182. Cf. also Cohnheim, Chemie 

 d. Eiweisskorper, 1900, p. 9. 



* Cohn, Beitr. z. Biol., 1877, Bd. ir, p. 266. 



5 Cramer, Centralbl. f. Bact., 1892, Bd. XI, p. 453. The resistance may be aided by the non- 

 absorption of water, and hence Pouchet found (Compt. rend., 1866, T. LXIII, p. 939) that the seeds 

 of Medicago were still capable of germination after being in boiling water for four hours. Similarly 

 the seeds of stone fruits that have been made into jam have been known to germinate. Cf. also 

 Nobbe, Samenkunde, 1876, p. 228. 



6 Certain combustions (viz. phosphorus in oxygen) only take place in the presence of a trace 

 of moisture. As regards the influence of the percentage of water upon the temperature of 

 coagulation of egg-albumin cf. Lewith, Centralbl. f. Physiol., 1890, Bd. IV, p. 382. 



7 For the literature see Nobbe, Samenkunde, 1876, p. 229; Kerner and Oliver, Natural History 

 of Plants, Vol. I, p. 554. 



8 Bialoblocki, Einfluss der Bodenwarme auf die Entwickelung einiger Culturpflanzen, 1872. 



