252 THE POWER OF RESISTANCE TO EXTREMES 



many cases not die more rapidly in such a medium than they do in air. 

 The same applies to seeds 1 , although they are injured if placed in these 

 media when moist, or if the media contain sufficient water to allow of a 

 certain degree of swelling. Absolute alcohol penetrates many resistant dry 

 seeds and spores with the utmost difficulty or not at all, as can be shown 

 by adding soluble pigments or chemical substances to the alcohol, and 

 examining the seeds after prolonged immersal. Some dry seeds (hemp, 

 peas, wheat) are penetrated more easily and are readily killed 2 . It is 

 possibly owing to their non-penetration that poisons dissolved in absolute 

 alcohol have little or no action on perfectly dry seeds 3 , and, similarly, dry 

 seeds are comparatively unaffected by exposure to poisonous gases 4 . As the 

 alcohol penetrates an oily seed, the oil is slowly dissolved out ; but this 

 takes a long time, even when the seed-coat is removed, and the seed is killed 

 long before. In the case of spores and bacteria it seems probable that all 

 the oil can be removed without vitality being destroyed. 



It is a fact of great biological importance that resistant seeds can with- 

 stand rapid drying and sudden moistening. Just as in the case of freezing and 

 thawing, so also is it possible that gradual moistening may favour revival 5 , 

 and on the other hand a diminution in the supply of water excites the 

 production of resistant spores in many plants. Here it is of importance 

 that the gradual drying should give sufficient time for the production of 

 the resistant organs. 



Seeds may become capable of withstanding desiccation while still 

 unripe, and even when they have not gained one-half their dry weight 

 when adult 6 . The seedling is, however, killed by drying, and the re- 

 sistance gradually decreases during germination. De Saussure 7 showed that 



1 Pasteur (Compt. rend., 1877, T. LXXXV, p. 99) found that the spores of Bacillus anthracis 

 remained living after twenty-one days in alcohol, and Bernard (Le9ons s. 1. phenomenes d. 1. vie, 

 1878, p. 54) found yeast-cells living after three to four clays in the same medium. Concerning seeds 

 cf. Nobbe, Samenkunde, 1876, p. 283. Hoffmann's remarks (Jahrb. f. wiss. Bot, 1860, Bd. II, 

 p. 331) are without value. Cf. Fltigge, Mikroorganismen, 1896, 3. Aufl., Bd. I, p. 450. 



2 Ewart, Vitality and Germination of Seeds, Trans. Liverpool Biol. Soc., Vol. VIII, 

 1894, pp. 222-229. 



3 Cf. Kronig and Paul, Zeitschr. f. Hygiene u. Infectionskrankheiten, 1897, Bd. xxv, p. 91. 



* Romanes quoted by Brown and Escombe, Proceedings of the Royal Society, 1897, Vol. LXII, 

 p. 160. 



5 Schroder, Unters. a. d. Bot. Inst. in Tubingen, 1886, Bd. n, pp. 45-7. In regard to seeds 

 cf. also Just, Cohn's Beitr. z. Biol., 1877, Bd. n, p. 338. De Saussure (Ann. d. sci. nat., 1827, T. X, 

 p. 92) states that the dried radicles only remain living when gradually moistened, but this needs con- 

 firmation. Cf. Schroder, 1. c. 



6 Schroder, 1. c., p. 10. On the germination of unripe seeds cf. Cohn, Symbola ad seminis 

 physiologiam, 1847, p. 39; Nobbe, I.e., p. 339; Kinzel, Landw. Versuchsstat., 1901, Bd. LV, 

 p. 255. The cells of unripe seeds shrink so that the reserve materials fill the remaining space (Pfeffer, 

 Jahrb. f. wiss. Bot., 1872, Bd. vnr, p. 510). 



7 De Saussure, Ann. d. sci. nat., 1827, T. X, p. 68 ; Schroder, 1. c., p. 1 2, and the literature there 

 given; Will, Versuchsstat., 1883, Bd. xxvm, p. 52; Bonnier, Rev. gen. d. Bot., 1892, T. iv, 

 p. 193 ; Frank, Krankheiten der Pflanzen, 1895, 2. Aufl., p. 263. 



