EFFECT OF MOISTURE AND TEMPERATURE. 25 



(h<> tcmjH'nitmv increases. Formerly the j-(Mieral consensus of opinion 

 lias been to make this statement in the reverse order that is, that 

 temperature exerts a veiy harmful action on seeds if much moisture 

 be present. For comparatively high temperatures the latter statement 

 would probably suffice at least it is not misleading, and in a certain 

 measure it is true; but at the lowest known temperatures, as well as 

 at ordinary temperatures, moisture is the controlling factor, and in 

 order to be consistent it should likewise be so considered for higher 

 temperatures that is, within reasonable limits. 



That temperature is only of secondary importance is brought out in 

 the results obtained bj^ a number of investigators. It has been well 

 established by Sachs, a Haberlandt,^ Just, c Krasau/ Isidore-Pierre/ 

 Jodin/, Dixon,* 7 and others that most seeds, if dry, are capable of 

 germination after being subjected to relatively high temperatures for 

 periods of short duration. The maximum for most seeds is a tempera- 

 ture of 100 Q C. for one hour; but if the seeds contain comparatively 

 large quantities of moisture they are killed at much lower tempera- 

 tures. It has been reported that lettuce seed will lose its vitality in 

 two weeks in some of the tropical climates where moisture is abundant. 

 Dixon has shown that if lettuce seed be dry it will not all be killed 

 until the temperature has been raised to 114 C. 



In case of low temperatures the factor of moisture is of less impor- 

 tance, yet even under such conditions the moisture must not be exces- 

 sive or the injury will be quite apparent. But if seeds are well 

 dried it can safely be said that they will not be killed as a result of 

 short exposures to the lowest temperatures which have thus far been 

 produced. Our knowledge of the resistance of seeds to extremely 

 low temperatures is based on the experiments of Edwards and Colin/* 

 Wartmann,* C. De Candolle and Pictet/ Dewar and McKendrick,* 

 Pictet,' C. De Candolle, Brown and Escombe, w Selby, and Thiselton- 



Handbuch d. Exp. Phys. d. Pflanzen, Leipzig, 1865, p. 66. 



'>Pflanzenbau I, 1875, pp. 109-117; Abs. in Bot. Jahresbr., 1875, p. 777. 



'Bot. Zeit., 33, Jahrg. 1875, p. 52; Cohn's Beitrage zur Biol. der Pflanzen, 1877, 

 2: 311-348. 



rfSitzungsbr. d. Wiener Akad. d. Wiss., 1873, 48: 195-208. I. Abth. 



< 'Ann. Agron., 1876, 2: 177-181; Abs. in Bot. Jahresbr., 1876, II. Abth., 4: 880. 



/Compt. Rend., 1899, 129: 893-894. 



(/Nature, 1901, 64: 256-257; notes from the Botanical School of Trinity College, 

 Dublin, August, 1902, pp. 176-186. 



/' Ann. sci. nat. bot., ser. 2, 1834, 1: 257-270. 



* Arch. d. sci. phys. etnat., Geneve, 1860, 8: 277-279; ibid., ser. 3, 1881, 5: 340-344. 



JIbid., ser. 3, 1879, 2: 629-632; ibid., ser. 3, 1884, 11: 325-327. 



*Proc. Roy. Inst., 1892, 12: 699. 



'Arch. d. sci. phys. etnat., Geneve, ser. 4, 1893, 30: 293-314. 



'"Ibid., ser. 4, 1895, 33: 497-512. 



Proc. Roy. Soc., 1897-8, 62: 160-165. 



ofiul. Torr. Bot. Club., 1901, 28: 675-679. 



