The Plantlet. 33 



in what position the seed is 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 best to 

 cover most seeds at planting, or at least to press them 

 well into the soil (51). In nature, seeds usually be- 

 come more or less covered, and these not covered gen- 

 erally fail to germinate. 



41. The Seed-Case in Germination. After germina- 

 tion commences, the seed-case is of no further use. It 

 has fulfilled its purpose, which is to protect the seed 

 from the time of its maturity until the conditions ar- 

 rive for germination, and is henceforth a hindrance to 

 germination in many plants, as it must be torn asunder 

 by the expanding plantlet. If we watch the germina- 

 tion of squash or pumpkin seeds through the different 

 stages, we may discover that nature has made a special 

 provision to help the plantlet in escaping from the seed- 

 case in these plants. As the hypocotyl curves down- 

 ward, a projection or hook is formed en the side toward 

 the seed, which holds the seed-case down while the seed- 

 leaves are pulled out from it. The action of this hook 

 is shown in the accompanying figures. Sometimes, as 

 shown in C, the point of the seed-case breaks, permit- 

 ting the hook to slip off, and if the seed happens to be 

 planted edgewise or with the point downward, the hook 

 often fails to catch the seed-case, as in D, and so the 



Often called radicle and caulicle. 



