22 THE PLANT. 



The conditions required for the germination of a 

 seed are moisture, a certain degree of heat, and access 

 of air ; where one of these conditions is excluded, the 

 seed will not germinate. By the influence of the moist- 

 ure which the seed absorbs, and which causes it to 

 swell, a chemical action takes place in it ; one of the 

 nitrogenous constituents acts upon the others, and upon 

 the amylum, so that by a transposition of the element- 

 ary particles, the constituents are rendered soluble ; the 

 gluten is converted into vegetable albumen ; the amy- 

 lum and oil into sugar. If the oxygen of the air is ex- 

 cluded, the changes either do not take place or they 

 proceed in a different way. The seeds of land-plants, 

 when submersed under water, or placed in a soil cov- 

 ered with stagnant water, which excludes the air, w r ill 

 not- put forth their plumules. This is the cause why 

 many seeds, lying deep in the ground or in bogs, will 

 remain for many years without germinating, although 

 the conditions of moisture and temperature be favour- 

 able. It is often found that earth taken up from bogs, 

 or brought up by the plough from the deep subsoil, and 

 exposed to the atmosphere, becomes covered with vege- 

 tation, arising from seeds which, for their develope- 

 ment, required free access of air. Lowness of tempera- 

 ture tends to annul or retard the influence of the air 

 upon the process of germination ; whilst increase of 

 temperature, with a proper supply of moisture, acceler- 

 ates the chemical changes in the seed. No seed germi- 

 nates below 32 Fahrenheit ; each germinates at a defi- 

 nite temperature, and therefore in fixed seasons of the 

 year. The seeds of Vicia fdba, Phaseolus vulgaris, 

 and the poppy, lose the power of germinating when 

 dried at 95 Fahrenheit ; while barley, maize, lentil, 

 hemp, and lettuce seed retain the power at that heat ; 

 but wheat, rye, vetch, and cabbage seed will germinate 

 even at 158 Fahrenheit. 



During germination, oxygen is taken up from the 

 air around the seed, and an equal volume of carbonic 

 acid is evolved. 



If seeds are set to germinate in glasses, with a slip 



