THE PROPAGATION OF PLANTS 133 



riety from seeds ; but most fruits and trees and 

 shrubs do not, and in such cases recourse 

 is had to bud propagation, as layers, cuttings, 

 grafts. 



2. Seedage, or Propagation by Seeds 

 2a. Requisites of germination 



216. In order that seeds shall germinate, the 

 seeds themselves must be viable (or "good"). 

 Viability depends upon (a) the maturity of the 

 seeds, (b) freshness, they shall not have lost 

 their vitality through age, (c) the vigor and 

 general healthfulness of the plant which bore 

 the seeds, (d) proper conditions of storage. 



217. (b) The length of time during which 

 seeds retain their vitality varies with the kind of 

 plant and with the conditions under which the 

 seeds were grown. That is, there is a normal 

 vitality and an incidental vitality. Most seeds 

 germinate best when not more than one or two 

 years old, but retain strong vitality three or 

 four years ; but some seeds, notably those of 

 onions and parsnips, are usually not safe after 

 a year old. 



218. In order that seeds shall germinate, 

 they must also have proper surrounding con- 

 ditions: moisture, free oxygen (air), warmth. 



