328 VEGETABLE PHYSIOLOGY 



it is so gradual that the water can be re-absorbed into the 

 cells, they may continue to live, but otherwise the organ is 

 killed. The cells become flaccid and the protoplasm at 

 once ceases to have the power of maintaining them in the 

 turgid condition. 



The effect of the absence of moisture in enabling 

 vegetable organisms to resist cold has recently been 

 examined in the case of seeds. Several kinds of these 

 have been found to be capable of germinating after immer- 

 sion for several hours in liquid hydrogen, the temperature 

 of which is the lowest at present known. 



A similar effect is found at the other end of the scale. 

 If seeds are heated very gradually some will withstand a 

 temperature of 98 C. The gradual loss of water is a 

 necessary condition for this immunity, for when the heating 

 is conducted so quickly that the water is not driven off at 

 a low or moderate temperature, the treatment is fatal in 

 all cases. Under conditions of gradual heating, their tem- 

 perature being maintained at 60 C. for twenty-four hours, 

 seeds have been found capable of germinating after a sub- 

 sequent exposure to 98 C. lasting for ten hours. 



Spores of bacteria and of fungi have a great power of 

 resisting high temperatures, and this is probably also asso- 

 ciated with a considerable degree of dryness. They can 

 withstand boiling in water for some time, but it is probable 

 that the reason why they are not destroyed is that their 

 walls successfully resist the passage of water into their 

 interior. 



We are unable at present to explain in detail the 

 causes of the death of protoplasm under the conditions of 

 extremes of temperature. We can only say that under 

 these conditions living substance ceases to carry out the 

 normal reactions which are characteristic of it so long as 

 it is what we call ' living,' and that the power to resume 

 them after the disappearance of the adverse conditions is 

 not regained by it. The nature of life and the intimate 

 causes and features of death are still beyond our knowledge. 



