166 



GEEMINATION 



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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 



284. The youug roots are not able to gain end rOOtS are emitted. The 



a foothold. elongating caulicle is known 



as the h3T)ocotyl ("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. Gemiiiuitiouof beau. 



the hypocotyl does not elongate greatly 

 and the cotyledons remain under 

 ground, the germination is hypogeal 

 ( " beneath the earth " ) . Pea and 

 runner bean are examples. 

 When the germinating seed lies on a 

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

 cot vl and rootlets mav not be able to seeiire a foothol<l 



285. Cotyledons of g 

 rating bp;\n spread apart gCQ^lgt 



to show elongating cauli- 

 cle and plumule. 



