254 THE POWER OF RESISTANCE TO EXTREMES 



seeds soon die when kept. Moreover dry mosses are not injured by immersal 

 in rancid fat or in oleic acid. The vitality of the dried plant appears to depend 

 not only upon its stage of development and whether it is ripe or not, but also 

 upon the cultural conditions and other circumstances. It is only in this way 

 that we can explain the unequal duration of vitality in the seeds or spores 

 of the same individual, as when some of the spores of Phycomyces nitens die 

 after a few weeks, but others not till after two or three years l . 



Many, but not all, seeds can withstand desiccation. For example, the seeds 

 of Oxalis rubella^ O. landfolia 2 , Coffea arabica, Dictamnus fraxinella, Angelica 

 archangelica, and of many Myrtaceae and Lauraceae, lose the power of germination 

 when thoroughly dried 3 . The seeds of willows commonly lose their vitality 

 in a few days, and hence Wichura 4 and Winkler 5 considered them to be incapable 

 of resisting desiccation. Wiesner 6 and Woloszczak 7 have, however, shown that 

 those willow seeds which remain living for more than three months can withstand 

 drying. 



The air-dried seeds of willows lose their vitality in a few months, but other 

 seeds not until after the lapse of some years. After ten years in dry air many seeds 

 are dead 8 , and but few are living after twenty-five years 9 . Nevertheless the seeds 

 of Nelumbitim were found to be still capable of germination after 100 years 10 . 

 Other seeds may live still longer, but the accounts of the germination of wheat 

 found in mummies are based on error, the wheat having been subsequently 

 introduced ". Burgerstein found that the carefully preserved seeds of barley, oats, 

 and wheat were mostly still capable of germination after ten years, although the 

 seeds of rye had lost their vitality in this time. 



The life of a pollen-grain is usually short, but in certain cases vitality may 

 be preserved for some length of time 12 . 



Vascular Cryptogams. Of these, Isoetes hystrix, Polypodium vulgare, and 

 Ceterach u withstand drying, and Wittrock found Selaginella lepidophylla to be still 

 living after it had lain in a herbarium for eleven years. Most of the spores are 

 also resistant to desiccation, and retain their vitality for a long time. The spores 



Schroder, Unters. a. d. Bot. Inst. in Tubingen, 1886, Bd. u, p. 34. 

 Hildebrand, Bot. Ztg., 1884, p. no. 



De Candolle, Pflanzenphysiol., trans, by Roper, 1835, B ^. II, p. 260; Schroder, 1. c., p. 8; 

 U. Dammer, Bot. Jahresb., 1897, p. 154. 



Wichura, Jahresb. d. schles. Ges. f. vaterl. Cultur, 1856, p. 56. 



Winkler, Bot. Jahresb., 1877, p. 352. 



Wiesner, Biol. d. Pflanzen, 1889, p. 43. 



Woloszczak, Bot. Centralbl., 1889, Bd. xxxix, p. 150. 



Cf. Nobbe, Samenkunde, 1876, pp. 37, 370. 



De Candolle, Ann. d. sci. nat, 1846, 3 e ser., T. vi, p. 373. 



10 Cf. de Candolle, Geographic botanique, 1855, p. 542. 



11 Burgerstein, Beobachtungen ii. d. Keimkraftdauer, &c. (repr. from Verh. d. Zool.-Bot. Ges. in 

 Wien, 1895). 



13 Cf. Mangin, Bull. d. 1. Soc. Bot. d. France, 23 juillet 1886; Rittinghaus, Verh. d. naturw. 

 Vereins d. Rheinlande, 1886, Bd. XLIII, p. 139. 



13 Braun, Verjiingungen, 1851, p. 213, footnote. 



14 E. Bureau, Compt. rend., 1890, T. ex, p. 318; Wittrock, Bot. Centralbl., 1892, Bd. XLIX, 



