OF SEED-SOWING. 159 



colour, odour, flavour, &c., so mucli depend. Some 

 suggestions by Mr. Knight, as to the manner in which 

 this result can be artificially produced, will be found 

 in the Hort. Trans., vol. iv. p. 2 and 3 : but the sub- 

 ject has yet attracted little attention. (See also Hort 

 Trans., new series, i. 34.) 



CHAPTEE V. 



OF SEED-SOWING. 



When a seed is committed to the earth, it under- 

 goes certain chemical changes (14) before it can de- 

 velope new parts and grow. These changes are 

 brought about by heat and water, assisted by the ab- 

 sence of light. In many seeds the vital principle is 

 so strong, that to scatter them upon the soil, and to 

 cover them slightly with earth, are suiiicient to ensure 

 their speedy germination ; but in others the power 

 of growth will only manifest itself under very favour- 

 able conditions ; it is, therefore, necessary to consider 

 well upon what the circumstances most suitable to 

 germination depend. 



Moisture is necessary, but not an unlimited quan- 

 tity. If seed is thrown into water and exposed to a 

 proper temperature, the act of germination will take 

 place; but, unless the plant is an aquatic, it will 

 speedily perish ; no doubt because its powers of respi- 



