MOVEMENTS OF THE SEEDLING 



23 



29. What pushes the Cotyledons up? — A very little 

 study of any set of squash seedlings is sufficient to show 

 that the portion of the plant where roots and hypocotyl 

 are joined- neither rises nor sinks, but that the plant grows 

 both ways from this part. It is evident that as soon as 

 the hypocotyl begins to lengthen much it must do one of 

 two things : either push the cotyledons 

 out into the air or else force the root 

 down into the ground as one might push 

 a stake down. What 



Fis. 9. Successive Stages in tlie Life History of the Bean Seedling. 



-44, the surface of the ground ; r, primary root ; ?•', secondary root ; 

 c, hypocotyl ; a, arch of hypocotyl ; co, cotyledons. 



changes does the plantlet undergo in passing from the 

 stage shown at A to that of B and of C, making it harder 

 and harder for the root to be thrust downward ? 



30. Use of the Peg Squash seedlings usually (though 



not always) form a sort of knob on the hypocotyl. This 



