250 THE POWER OF RESISTANCE TO EXTREMES 



condition. The vegetative organs of a few vascular Cryptogams are able, 

 however, to withstand desiccation, and the same power is possessed by those 

 mosses and lichens which are often subjected to severe drought in their 

 natural habitats. Lichens afford instances of both algae and fungi resistant 

 to desiccation, to which, however, the vegetative parts of most algae 

 which grow submerged in water succumb. It is worthy of note that the 

 combination of alga with fungus seems to increase the resistant power of 

 the former to desiccation and dry heat as well as to insolation 1 . The 

 vegetative parts of most fungi are readily killed by desiccation, which, 

 however, most of the spores and perennating organs can withstand. The 

 same applies to bacteria, and here, as in a few fungi, the vegetative parts 

 are resistant to desiccation. 



All turgid plants can withstand a certain loss of water, and all grades 

 of resistance are shown in different plants. Even those which are most 

 sensitive may survive a loss of from 40 to 50 per cent, of water, and 

 the vegetative organs of some flowering plants are not killed by a loss 

 of from 80 to 90 per cent. 2 The latter is usually the case in plants 

 naturally subject to temporary drought, independently of the amount of 

 water they normally contain. Schroder 3 found that the succulent Sedum 

 elegans with 16 per cent, of dry substance could withstand the loss of 

 9t> but not 95 per cent, of its water, whereas the more sensitive leaves of 

 Parietaria arbor ea were partly killed by a loss of 50, and entirely by a loss 

 of 70 to 76 per cent, of their water. Only approximate estimations are, 

 however, possible, since a loss of water which is not at first fatal may prove 

 so after a time, and further the cells and organs which absorb water with 

 the greatest energy draw upon the other parts and cause these to shrivel 

 and die prematurely. 



Many Cryptogams can withstand air-drying but not desiccation over 

 sulphuric acid or phosphorus pentoxide 4 . The aquatic moss Fontinalis 

 antipyretica is killed by air-drying, whereas Mnium hornum, which grows 

 in fairly moist localities, resists several weeks' air-drying. This moss and 

 also the somewhat more resistant Fnnaria hygrometrica soon die in 

 a desiccator, in which Barbitla muralis, Brynm caespiticium, and other 

 mosses which grow in dry habitats may remain living for more than twenty 

 weeks. Similar grades of resistance 5 are shown by various species of 

 Oscillaria, and by bacteria. The mosses and lichens which grow on rocks 



1 Ewart, Journ. of Linn. Soc., 1896, Vol. XXXI, pp. 375, 376, 383. 



3 In the case of a turgid plant containing So per cent of water, a loss of weight of 32 to 40 per 

 cent, represents 40 to 50 per cent, of water ; one of 72 per cent., a loss of So to 90 per cent, of water. 



3 Schroder, Unters. a. d. Bot. Inst. in Tubingen, 1886, Bd. II, p. 5 ; Dutrochet, Mem. p. 

 servir a 1'histoire d. v^g^taux et des animaux, 1837, p. 204; de Candolle, Pflanzenphysiol., trans, 

 by Roper, 1835, Bd. n, p. 872 ; Fleischer, Bot. Centralbl., 1885, Bd. xxn, p. 356. 



4 Schroder, 1. c. ; Ewart, Trans. Liverpool Biol. Soc., 1897, Vol. XI, p. 151 ; Koch's Biol. 

 Centralbl., 1892, Bd. xn, p. 336. 5 Schroder, 1. c., pp. 15, 32. 



