MORPHOLOGY OF THE SEEDLING 27 



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 (a little 

 above r' in Fig. 9, A and B). 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 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? 



35. Use of the Peg. — Squash seedlings usually (though 

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

 known as the peg. Study a good many seedlings and try 

 to find out what the lengthening of the hypocotyl, between 

 the peg and the bases of the cotyledons, does for the little 

 plant. Set a lot of squash seeds, hilum down, in moist 

 sand or sawdust and see whether the peg is more or less 

 developed than in seeds sprouted lying on their sides, and 

 whether the cotyledons ip the case of the vertically planted 

 Seeds usually come out of the ground in the same condi- 

 tion as do those shown in Fig. 9. 



36. Discrimination between Root and Hypocotyl. — It is 

 not always easy to decide by their appearance and be- 

 havior what part of the seedling is root and what part is 

 hypocotyl. In a seedling visibly beginning to germinate, 

 the sprout, as it is commonly called, which projects from 

 the seed might be either root or hypocotyl or might consist 

 of both together, so far as its appearance is concerned. A 

 microscopic study of the crossnsection of a root, compared 

 with one of the hypocotyl, would show decided differences 



