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° 

 Pahr. ). 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 arc 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 water, 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. 37. 



