36 Principles of Plant Culture. 
hence the cotyledon is not lifted. The tiny pointed shoot 
(plumule, 56) of these plants readily insinuates itself between 
the soil particles and comes to the surface, with little expend- 
iture of energy, even when deeply planted. Plantlets of the 
larger beans usually fail if the seeds are planted three 
inches deep in a clay soil that bakes above them. Those of 
the castor bean (Ricinus), though very robust, can hardly 
lift their cotyledons through one inch of soil, while those of 
the pea, though much more slender, readily grow through 
four to six inches. Apple seeds planted in autumn, on clay 
soil, usually fail to germinate the following spring, unless 
covered with sand or humus, or carefully mulched, because 
the plantlets are unable to lift their cotyledons through a 
baked surface soil. 
49. The Vigor of the Plantlet is generally in Propor= 
tion to the Size of the Seed. This is true, not only be- 
tween different kinds of seeds, but between different indi- 
vidual seeds of the same kind. The larger beans, the horse 
chestnut and the walnut form very much stronger plaxtlets 
than clover, timothy and tobacco, and the largest and 
plumpest specimens of any sample of seed usually form 
stronger plantlets than the smaller and more shrunken speci- 
mens. Growers of lettuce under glass are sometimes able 
to raise one more crop during the winter by sowing only 
the largest seeds than when the seed is sown without sift- 
ing. The practice of sifting seeds before planting, and re- 
jecting the smaller specimens, should be more generally 
followed. 
50. The Earlier Germinations from a sample of seed 
usually Form More Vigorous Seedlings than the Later 
Ones. This is nature’s method of preserving the vigor of 
