166 



GERMINATION 



284. The young roots are not able to gain 



a foothold. 



other to remain empty. In a day or two insert a lighted 

 splinter or taper into each. In the empty jar the taper 



burns: it contains Oxygen. 

 In the seed jar the taper 

 goes out: the air has been 

 replaced by carbon dioxid. 

 Usually there is a percepti- 

 ble rise in temperature in a 

 mass of germinating seeds. 



311. The caulicle usually 

 elongates, and from its lower 

 end roots are emitted. The 

 elongating caulicle is known 

 as the hypocotyl ("below the cotyledons"). That is, the 

 hypocotyl is that part of the stem of the plantlet lying 

 between the roots and the coty- 

 ledon. The general direction oj 

 the young hypocotyl or emerging 

 caulicle is downwards. As soon 

 as roots form it becomes fixed, 

 and its subsequent growth tends 

 to raise the cotyledons above the 

 ground, as in the bean. When 

 cotyledons rise into the air, germ- 

 ination is said to be epigeal 

 ("above the earth"). Bean and 



pumpkin are examples. When 286. Germination of bean. 



the hypocotyl does not elongate greatly 

 i ^wS!X and the cotyledons remain under 



ground, the germination is hypogeal 

 ( " beneath the earth " ) . Pea and 



285. Cotyledons of germi- v 



nating bean spread apart SC arlet runner bean are examples. 



to show elongating cauli- 



cie and plumule. When the germinating seed lies on a 



hard surface, as on closely compacted soil, the hypo- 

 cotyl and rootlets may not be able to secure a foothold 



