188 



BOTANY. 



According to several observers, the minima and optima 

 for the germination of the seeds of the following plants are : 



246. Death Caused by High Temperature. When the 

 temperature rises above a certain point the death of the 

 plant takes place. Those plants, or parts of plants, which 

 contain the least water are capable of enduring higher tem- 

 peratures than those which are more watery. Thus at from 

 65 to 80 Cent. (149 to 177 Fahr.) many dry spores and 

 seeds are uninjured, while in water they are generally killed 

 when the temperature exceeds 50 or 55 Cent. (122 or 131 

 Fahr.). For ordinary growing parts of plants the tempera- 

 ture must be, as a rule, considerably lower than those given 

 above. Few aquatic plants can endure a prolonged tempera- 

 ture much, if any, above 40 Cent. (104 Fahr.), and at 50 

 Cent. (122 Fahr.) most terrestrial plants are soon killed. 

 It appears, also, that at temperatures much lower than these 

 some plants are killed ; thus, according to Hofmeister,* the 

 organization of the protoplasm of the plasmodium of Didy- 

 mium serpula (one of the Slime Moulds) is destroyed by 

 heating it, in air, to 35 Cent. (95 Fahr.), and in the nearly 

 related Fuligo varians the same destruction follows at 39 

 Cent. (102 Fahr.). 



The immediate cause of death appears to be the coagula- 

 tion of the albuminoids of the protoplasm. The protoplasm 

 thus loses its power of imbibing Avater, and the cells conse- 

 quently lose their turgidity. In watery tissues chemical 

 changes at once begin, resulting in the rapid disintegration 



* " Die Lehre von der Pflanzenzelle," 1867, p. 27. 



