The Flantlet. 33 



41. The Hypocotyl* (hy'-po-co'-tyl) Grows Downward, 



on emerging from the seed-case (27d), no matter 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, be^ 

 cause 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 (52). In nature, seeds usually become more or less 

 covered, and those not covered generally fail to germinate. 



42. The Seed-Case in Germination. After germination 

 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 arrive for 

 germination, and is henceforth a hindrance to germina- 

 tion in many plants, as it must be torn asunder by the 

 expanding plantlet. If we watch the germination of 

 squash or pumpkin seeds through the different stages, 

 we may discover that nature has made a special provis- 

 ion to help the plaiitlet in escaping from the seed- case 

 in these plants. As the hypocotyl curves downward, a 

 projection or hook is formed on 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, permitting the hook 

 to slip off, and if the seed happens to be planted edge- 

 wise or with the point downward, the hook often fails 



* Often called radicle and caulicle. 



