OF PLANTS. Vl 



cci.t germ. Some seeds are farther protected 

 by a hard outer covering; but this remark ap- 

 plies only to the seeds of trees. Although 

 the gradations from the hard external shell of 

 the apricot stone, to the membranous cover- 

 ing of the wheat are so gradual, that the line 

 where the one begins and the other encjs, is 

 difficult to be decided on, and indeed whether 

 inclosed in the shell or membrane, the changes 

 ail seeds undergo in the process of germinating, 

 seems to be precisely the same, and it may be 

 worthy of notice here, that so effectual is the 

 membranous covering in protecting the germ 

 from injury, that seeds found in the mummies 

 taken from the pyramids of Egypt, which 

 must be at least 3000 years old, have vegetated, 

 when planted in favourable circumstances; and 

 farther, seeds brought up from the interior of 

 the earth in sinking wells, mines, and other 

 excavations have also germinated, although the 

 period when such seeds could have been depo- 

 sited in such positions is altogether beyond hu- 

 man conception. 



The circumstances necessary for the germi- 

 nation of the seed depend externally on heat, 

 moisture, air, soil and situation ; although these 

 two latter conditions are not in all cases indis- 

 pensable. 



Moisture is absolutely necessary for the seed 

 when planted, its first action is to swell by ab- 

 sorbing the pulpy matter of the pod, which 

 then bursts open and allows the air to act in 

 concert with the water thus absorbed, in cre- 

 ating new compounds, such as starch, sugar, 



3* 



