DESICCATION 



253 



radicles which had just escaped could still withstand air-drying, but not 

 in all cases drying over sulphuric acid. When the radicle becomes as 

 long or longer than the seed, its resistance to desiccation is lost, but the 

 seedling may replace it by adventitious roots if it is destroyed. It is 

 worthy of note, however, that a sowing of grass is injured more by drought 

 just after germination than when the roots have penetrated more deeply into 

 the soil. As in the case of seeds, the germ-tubes formed by the resistant 

 spores of Penicillium, Phycomyces, Mucor 1 , and Uredo ' 2 are killed by drying. 



The means by which the power of resistance to drying is gained, and 

 the changes which cause its loss, are quite unknown. There is no direct 

 connexion between the storage of food-materials and the resistance to 

 desiccation, for all cells filled with food-materials cannot resist drying, and 

 the leaves of mosses remain resistant even when starved 3 . 



The germination of unripe seeds also shows that resistance to 

 desiccation does not involve the complete filling of the cells with food- 

 materials. The latter has, however, a certain advantage, since it prevents the 

 shrivelling and crumpling of the cells which those in the leaves of mosses 

 undergo* on drying. The protoplasm in the leaf-cells of mosses is shown 

 to be rich in water by its contraction on drying, so that a high percentage 

 of water is compatible with a power of resistance to desiccation. Nor need 

 the protoplasm be impregnated with fat or oil 4 . Since full turgor is 

 restored in mosses and other plants immediately after moistening them, 

 it is evident that the osmotic materials remain as solids in the central 

 vacuole. Evidently therefore the protoplasm is not injured by the con- 

 centrated cell-sap. If, however, the latter is responsible for the death of 

 certain plants on drying, we have revealed to us in such cases the 

 immediate cause of the fatal action of desiccation. It is, however, hardly 

 likely that the death of plants killed by the removal of more or less of the 

 imbibed water, as well as that of those only killed by the removal of 

 the last traces of absorbed or even combined water, are alike produced 

 in the same way. 



The high resistance of dried plants to heat and cold, to alcohol and 

 other poisons, can easily be understood as the result of their diminished 

 powers of reaction, but the changes have still to be discovered which produce 

 their ultimate death. This is not due to the turning rancid of stored fats, 

 for although many oily seeds soon lose the power of germination, others, and 

 also oily spores, may retain their vitality for a long time, while many starchy 



1 Schroder, Unters. a. d. Bot. Inst. in Tubingen, 1886, Bd. n, p. 34; Nordhausen, Jahrb. f. 

 wiss. Bot., 1899, Bd. xxxill, p. 29 ; Duggar, Botanical Gazette, 1901, Vol. xxxi, p. 65. 



3 Hoffmann, Jahrb. f. wiss. Bot., 1860, Bd. II, p. 329. 



3 Schroder, 1. c., p. 45. 



* On the fats of mosses cf. Jb'nsson and Olin, Lunds Univ. Arsskr., 1898, Bd. xxxiv, Afd. 2, 

 Nr. I. 



