22 STRUCTURE AND FUNCTIONS 



resin, &c. which form the pabulum or nou- 

 rishment necessary for the young plant in its 

 first stage of existence, and before its organs 

 are sufficiently developed to obtain a supply of 

 food elsewhere. 



Heat follows next, and is equally indispen- 

 sable to the germination of the seed. A tem- 

 perature below 32° or much above 120° are 

 the extremes, beyond which vegetation does 

 not take place ; in the one case from the freezing 

 or extreme cold, closing the pores of the seed 

 to the moisture, and in the latter from the ex- 

 treme heat, causing the fluids of the seeds to 

 be too much expanded, when decomposition of 

 the parts takes, place. 



Air is also an essential ingredient in the ger- 

 mination of seeds, from the presence of its oxy- 

 gen. And it is probable, to the absence of 

 this cause, that seeds found buried in the earth, 

 under what would otherwise be considered fa- 

 vourable circumstances for their growth, have 

 lain so long dormant. 



Light, so necessary to the favourable growth 

 of the plant itself, is prejudicial to the deve- 

 lopment of the germ, from its power of disen- 

 gaging the oxygen necessary to the vitality of 

 the embryo of the plant. 



Soil and situation need not here be discussed, 

 as these attributes will be considered more at 

 large in the ensuing chapters. 



Electricity is also presumed to have an im- 

 portant effect in causing the germ to vegetate 

 and assume the functions of an organized plant, 

 but as yet this is only a surmise. The know- 



