264 DISPERSION OF SEEDS. [BOOK n. 



that 35 ceiitig. forms the highest limit of temperature which 

 corn can bear under such circumstances. But, in sand or 

 earth, the same grains sustained a prolonged temperature of 

 40 centig. (104 Fahr.) without inconvenience ; at 45centig. 

 (113 Fahr.) a great part perished ; at 50 centig. (122 Fahr.) 

 the whole of them. 



These remarkable experiments are calculated to throw 

 great light upon the cause of the impossibility of making 

 certain plants multiply themselves by seeds in hot countries. 

 If Wheat, Barley, &c., cannot endure a prolonged tempera- 

 ture above 40 centig. ; and the temperature of the soil is in 

 some countries and soils as high as 60 centig. ( 140 Fahr.), 

 as Humboldt asserts, or between 48 and 53 centig. (122 

 Fahr.), even in some parts of France, as Arago states; it 

 is evident that the seeds of corn placed in such situations will 

 perish. 



Some seeds will, however, bear a very high temperature 

 with impunity. Those of New Holland Acacias germinate 

 readily after having been boiled for as long as five minutes, 

 perhaps in consequence of the softening of their skin and 

 tissues; and a case is mentioned by Mr. Hemingway, 

 (Ann. of Nat. History, vol. viii. p. 317), of the seeds of the 

 Elder (Sambucus) which germinated readily after they had 

 twice been boiled in making wine, had been present during 

 the vinous fermentation, and had been allowed to remain 

 among the dregs of the wine bunged up in the cask for 

 a period of twenty months. In like manner the seeds of 

 the Raspberry have been known, to retain their vitality 

 after being boiled in sugar, in the operation of making 

 raspberry-jam. 



Exposed to the influence of water, heat, and air, the parts 

 of a seed soften and distend ; the embryo swells and bursts its 

 envelopes, extending the neck and the bases of the cotyledons, 

 and finally emitting its radicle, which pierces the earth, de- 

 riving its support at first from the cotyledons or albumen, but 

 subsequently absorbing nutriment from the soil, and commu- 

 nicating it upwards to the young plant. The manner in which 

 the embryo clears itself from its integuments differs in various 



