The Planitlet. 3I 
the majority have germinated. Seeds of tobacco and purs- 
lane* sometimes continue to germinate through several suc- 
cessive seasons. The reasons for these great variations in 
the time required for germination are not well understood. 
Section III. THE PLANTLET 
By watching the germination of seeds, we may learn some 
interesting facts. Good seeds will usually germinate freely 
on the surface of well-moistened soil or sand, if we provide 
a damp atmosphere above them by covering with a bell 
glass; for light does not hinder germination. One of the 
interesting facts connected with germination is, that the 
first shoot, called 
41. The Hypocotyl* (hy’-po-co’-tyl) Grows Down- 
ward, on emerging from the seed-case (72d), no matter in 
what position the seed was placed. It will curve in a semi- 
circle if necessary, to bring its rounded point in contact with 
the soil. But the hypocotyl is not always able to enter the 
soil, unless the seed is covered more or less, because the 
resistance offered by the soil is often greater than the weight 
of the seed. On this account, as well as to insure a supply 
of moisture, it is always best to cover seeds at planting, or 
at least to press them well into the soil (52). In nature, 
most seeds become more or less covered, and those not cov- 
ered usually fail to germinate. 
42, The Seed-Case in Germination. After germina- 
tion commences, the seed-case is of no further service. It 
has fulfilled its purpose, which is to protect the seed from 
the time of its maturity until the conditions arrive for ger- 
* Portulaca oleracea. 
7 Often called radicle and caulicle. 
