CHAPTER III 



MOVEMENTS, DEVELOPMENT, AND MORPHOLOGY OF 

 THE SEEDLING 



28. How the Seedling emerges — As the student has 

 already learned by his own observations, the seedling 

 does not always push its way straight out of the ground. 

 Corn, like all the other grains and grasses, it is true, sends 

 a tightly rolled, pointed leaf vertically upward into the 

 air. But the other seedlings examined usually will not 

 be found to do anything of the sort. The squash seedling 

 is a good one in which to study what may be called the 

 arched hypocotyl type of germination. If the seed when 

 planted is laid horizontally on one of its broad surfaces, it 

 usually goes through some such changes of position as are 

 shown in Fig. 9. 



The seed is gradually tilted until at the time of their 

 emergence from the ground the cotyledons are almost 

 vertical. The only part above the ground-line at this 

 period is the arched hypocotyl. Once out of ground, the 

 cotyledons soon rise until they are again vertical, but with 

 the ends farthest from the hypocotyl at the top. Then 

 the two cotyledons separate until they once more lie hori- 

 zontal, pointing away from each other. 



Can you suggest any advantage which the plant derives 

 from having the cotyledons dragged out of the ground 

 rather than having them pushed out, tips first? 



22 



