238 THE POWER OF RESISTANCE TO EXTREMES 



Instances of specific resistance have already been given in the case of flowering 

 plants 1 . Very many lichens are extremely resistant to cold, and the same 

 applies to many algae. Thus Goppert 2 found that the red snow organism 

 Sphaerella nivalis was not affected by a temperature of 36 C. Schumann 3 found 

 that diatoms remained living at 20 C, and Pictet 4 even at 200 C. All diatoms 

 do not behave similarly, and the resistance is least when growth is most active. 

 Thus Ewart 5 found that the actively vegetating forms of various diatoms were killed 

 by freezing at 8 to ToC. Our indigenous species of Spirogyra, Cladophora^ 

 and Vaucheria are relatively sensitive to cold when actively vegetating, and usually 

 only the oosperms or zygotes can resist actual freezing 6 . Many algae with a low 

 minimum for growth are readily killed by frost, and indeed some of the algae from 

 warm seas may possibly die at temperatures above zero. 



Fungi. Many species of Polyporus can withstand the severest winter cold, 

 whereas various Agaricineae are readily killed by frost r . In all cases the spores 

 appear to be highly resistant, and according to Chodat 8 the spores of Mucor 

 mucedo are not killed by exposure to a temperature of 1 10 C. Chodat's statement 

 that the vegetative mycelium of Mucor is equally resistant requires further proof, 

 since it is readily killed by the withdrawal of water, although encysted portions 

 ('endospor.es') may remain living. Further, Hoffmann 9 has shown that the 

 mycelia of Penicillium and Botrytis are readily killed by freezing. The plasmodia 

 of Aethalium and other Myxomycetes are unable to withstand severe cold 10 , and 

 small Amoebae appear always to be killed when ice forms in them n . 



Bacteria are so resistant, even in the vegetative condition, that they are 

 probably hardly ever killed by natural cold. Only a few species were killed by 

 prolonged exposure 12 , and neither the spores nor the vegetative cells of a variety of 

 forms were killed by an exposure of several hours to 200 C. 13 Pictet and Yung 14 , 

 however, found that Micrococcus luteus and the vegetative cells of Bacillus anthracis 

 were killed by an exposure of 108 hours at 70 C, and then twenty hours at i3oC, 

 whereas the spores of Bacillus anthracis^ B. subtilis, B. ulna were unaffected. 



1 On varieties resistant to frost cf. Noll, Landw. Jahrb., 1885, p. 708. On pollen-grains cf. 

 Rittinghaus, Verb. d. naturw. Vereins d. Rheinlande, Jahrg. 43, 5. Folge, Bd. HI, p. 164. 

 3 Goppert, Bot. Ztg., 1875, p. 615. 3 Quoted by Goppert, 1. c. 



* Pictet, Archives d. sci. phys. et nat. d. Geneve, 1893, 3 se>., T. xxx, p. 311. 



5 Ewart, Annals of Botany, 1898, Vol. xn, p. 366. 



6 Id., 1. c. ; W. Went and G. S. Went, Annals of Botany, 1898, Vol. xil, p. 33 ; Molisch, Das 

 Erfrieren d. Pflanzen, 1897, p. 21. 



7 Cf. Schmitz, Linnaea, 1843, Bd. XVII, p. 445; Fries, Ann. d. sci. nat., 1859,4 s ^r., 

 T. xn, p. 304; Goppert, I.e., p. 614; Ueber das Gefrieren und Erfrieren d. Pflanze, 1883, 



P- 57- 



8 Chodat, Bull. d. 1'Herbier Boissier, 1896, T. iv, p. 894. 



9 Hoffmann, Jahrb. f. wiss. Bot., 1860, Bd. n, p. 321. Cf. also Molisch, 1. c., 1897, p. 18. 



10 Kiihne, Unters. u. d. Protoplasma, 1864, p. 88. " Molisch, 1. c., p. 47. 



12 Cf. Fliigge, Mikroorganismen, 1896, 3 Aufl., Bd. I, p. 440. 



13 Schuhmacher, Sitzungsb. der Wiener Akad., 1874, I. Abth., Bd. LXX, p. 177 (-113 C. with 

 ether and solid carbon dioxide); Frisch, ibid., 1880, Bd. LXXX, III, p. 77; Pictet, 1. c. (up to 

 200 C.); Dewar and McKendrick, Royal Soc. Proc., 1892, Vol. xill, p. 699 (-182 C.) ; 

 Meyer, Centralbl. f. Bact., 1900, i. Abth., Bd. xxvin, p. 594. 



14 Pictet and Yung, Compt. rend., 1884, T. xcvni, p. 747. 



