30 



PRINCIPLES OF PLANT CULTURE 



different kinds of seeds, but often between different seeds of 

 the same kind. The larger beans, the horse chestnut and 

 the walnut form much stronger plantlets than clover, 

 timothy and tobacco, and fully developed specimens of 

 any sample of seed usually produce stronger plantlets 

 than the smaller and more shrunken specimens. Growers 

 of lettuce under glass are sometimes able, by sowing only 

 the largest seeds, to raise one more crop during the winter 

 than when the seed is sown without sifting. The practice 

 of sifting seeds before planting, and rejecting the smaller 

 ones, should be more generally followed (Fig. 13). Fre- 

 quently large seeds contain more food material than the 



Fig. 13. — Radishes grown from heavy and hght seeds. 



plantlet needs for best development. Such seeds will not 

 produce more vigorous plants than smaller seeds contain- 

 ing enough food material for the needs of the plantlet. 



49. Vigorous seedlings. — The earlier germinations 

 from a sample of seed often form more vigorous seedlings 

 than the later ones. This is one of nature's methods for 

 preserving the vigor of plants. The stronger seedlings 

 overtop the later and feebler ones and crowd them out of 

 existence. We should profit by this hint and reject the 

 later plants in the seed-bed. 



50. How deep should seeds be planted ? — We have 

 seen that one object of planting seeds in the soil is to place 

 them in contact with moisture (29). Since the plantlet 



