FRKEZING ÄND BURNING. 



555 



possible, are not killed even at the boiling point of water. Of various seeds from 

 which water has been withdrawn for fifty hours, and which have then been 

 heated for three hours up to 100^, those of duckweeds (49 per cent of the seeds 

 experimented upon) still germinated; of vetches, 50 per cent; of garlic, 60 per cent; 

 of wheat, 75 per cent; of sweet marjoram, 78 per cent, and of melons 96 per cent. 

 Even of seeds previously dried, which had been exposed for about fifteen months 

 to a temperature of 110° to 125°, a small percentage always germinated, and it is 

 possible that there are species whose seeds bear without injury still higher 

 temperatures. 



From these experiments it is clearly shown that the albuminous substances 

 in the protoplasm may give up with impunity much water, and that by this 



Fig. 137. — Edible Lichen {Lecanora esculenta) in the desert. 



surrender a protection is obtained against coagulation and burning, up to a certain 

 point. 



In nature, most contrivances by which plants are protected against burning 

 amount in reality to a periodic surrender of water. Lithophytes, especially crus- 

 taceous lichens, which are most threatened with the danger of being burnt, are 

 so organized that they can give up a great deal of water in a very short time. 

 They then become stiff" and brittle, and can be rubbed into powder, and it appears 

 scarcely credible that these dried-up structures can ever live again. In the rock- 

 lichens the same thing occurs. Also several Volvocineae, Sphterella pluvialis, 

 and various other simply organized plants, living in shallow pools and ditches, 

 dry up to dust along with the mud, after the evaporation of the water which had 

 accumulated in their habitat, and are protected in this dried condition against 

 burning. If the dust, which is warmed daily for several hours up to 60 during 

 the period of drought, becomes moistened later on, all the tiny plants wake up 

 again from their trance, and, as should not be overlooked, the rotifers and various 

 infusoria, which are present in the same heated dust, again bestir themselves, 

 flourish their cilia, and give evidence that the surrender of water at the right 

 moment affords the best protective measure against " burning " for animal proto- 



