Sentence:  A marked bud-variation is of very rare occurrence, but in many cases the tendency of plants raised from seeds to differ from the parents is so great that choice varieties are <WSD>propagated</WSD> entirely by buds. It is almost hopeless to attempt to <WSD>propagate</WSD> a choice variety of grape or strawberry by seeds, as the individuals raised in this way seldom have the valuable qualities of their parents, and, although they may have new qualities of equal or greater value, the chances are of course greatly against this, since the possibility of undesirable variation is much greater than the chance of a desirable sport. 
Meaning of the word marked with <WSD> tags:  To cause to continue or multiply by generation, or successive production