GENERAL PKINCIPLES. 



2d. Heat is the next most important element. Seeds 

 do not grow in winter. We sow our apple, pear, peach, 

 and 2>lum seeds in November, but they show no signs of 

 germination until a cliange of season. When the warmth 

 of spring penetrates the soil, it reaches the seed, and, in 

 connection with the moisture already imbibed, induces 

 chemical changes, which excite tlie vital energies of the 

 germ, decompose the mealy part of the seed, and prepare 

 it for the temporary nutrition of the young jilant. 



3d. Air. — Although seeds may have heat and moisture 

 in the requisite proportions, still it has been proved, by 

 many experiments, that without air, germination cannot 

 take place. 



Practical cultivators are aware that seeds planted too 

 deeply do not grow ; many kinds will lie buried in the 

 ground for years without growing, and when turned up 

 near the surface, will germinate immediately. It is the 

 oxygen of the air that constitutes its importance ; it pro- 

 duces, by forming new combinations with the constituents 

 of the seed, that chemical process which converts the 

 starch into gum and sugar, as we observe in ordinary 

 cases of fermentation. 



4th. Exclusion of Light. — The manner in which self- 

 sown seeds in the forest are covered with fallen and de- 

 caying foliage, plainly indicates that nature never intend- 

 ed the light to strike germinating seeds. A seed entirely 

 exposed would be at one time saturated with moisture, 

 and at another parched with drouth ; chemical changes 

 would be alternately promoted and checked, until the 

 vital principle would be destroyed, or so weakened as to 

 produce a feeble and worthless plant. The depth of the 

 covering should always be regulated by the size of the 

 seeds. Small and delicate seeds may be sown almost on 

 the surface, whilst large ones may be imbedded to the 

 depth of four or five inches. The small seed requires lit- 

 tle moisture, and has but a feeble force to penetrate an 



