DESICCATION 251 



must often become completely dry, wKereas plants rooted in soil rarely 

 lose all their water, except in the case of a few desert plants exposed to 

 long periods of intense drought and heat. Under ordinary circumstances, 

 however, the fall of dew at night enables the shrivelling plants to absorb 

 a certain amount of water. 



In ordinary air, dried plants retain from 8 to 14 per cent, of water, which 

 is not fully removed even in a desiccator 1 . Thus seeds may retain from 

 i to 3 per cent, and Stictapulmonacea as much as 4-8 per cent, of water, which 

 is gradually lost when the objects are heated to 100 or noC. in dry air. 

 Independently of whether this water is chemically bound or is merely water 

 of imbibition, it is not surprising that complete drying kills organisms which 

 are able to withstand drying over sulphuric acid 2 . The death of various 

 seeds, spores, and mosses at 100 C. may in fact be partly due to the 

 removal of the last traces of absorbed or combined water. This is, however, 

 not always fatal, for some organisms can withstand heating to a tempera- 

 ture of from 100 to 110 C. for several hours, and although thick seeds might 

 still not have lost all their water, this could hardly be the case when spores, 

 mosses, bacteria, and other small objects are used. Many spores, bacteria, 

 and a few seeds such as cress and linseed remain living after several weeks' 

 or even months' immersal in absolute alcohol, which must certainly remove 

 nearly all the water they contain. 



Dry plants ultimately die, although since they do not respire no 

 external change affords evidence of death. Many dry seeds, spores, and 

 mosses die in a short time, whereas others may live for many years, and 

 possibly for more than a century. The part played by the external 

 conditions in determining the preservation of vitality has not yet been 

 precisely determined, but the degree of desiccation is doubtless of impor- 

 tance. Such plants as Mnium hormim, Funaria, and Cladonia die more 

 rapidly in a desiccator than in ordinary air. Some plants may, however, 

 remain living longest when completely dried, and Schroder in fact found 

 (1. c., p. 34) that the spores of Phycomyces nitcns retained their vitality as long 

 in a desiccator, and in the absence of oxygen, as in ordinary air. Ficker 3 has 

 also shown that certain bacteria ( Vibrio cholerae, Bacillus typhi) live longer 

 in a desiccator than when alternately exposed to moist air and to the dry 

 air of a desiccator. 



The dry spores of Aspergillus niger, Phycomyces nitcns, of yeast, and 

 of bacteria are injured but little or not at all by prolonged immersal in 

 absolute alcohol, ether, benzol, and carbon bisulphide, and possibly may in 



1 Schroder, Unters. a. d. Bot. Inst. in Tubingen, 1886, Bd. II, p. 5 ; Evvart, Trans. Liverpool Biol. 

 Soc., 1897, Vol. XI, p. 151. 



2 The death of living frozen plants on a further lowering of the temperature is probably wholly 

 or in part due to the increased withdrawal of water. 



3 Ficker, Ueber Lebensdauer u. Absterben von pathogenen Keimen, Habilitationsschrift, 1898, 



P- 25- 



