lOO 



PHYSIOLOGY. 



doinp by a hard surface. After the root is 2-4COT long, and the 

 two lialves of the seed coats have begun to be jjried ajiart, if we 



look in this rift at the 

 junction of the root 

 and stem, we shall see 

 that one end of the seed 

 coat is caught against 

 a heel, or "peg," 

 which has gniwn out 

 frcjin the stem for this 

 urpose. Now if we 

 examine one which is 

 a little 

 more ad- 

 vanced, 

 we shall see this heel 

 more distinctly, and 

 also that the stem is 

 arching out away from 

 the seed coats. As the 

 stem arches up its back 

 in this way it pries w-ith 

 the cotyledons against 

 the upper seed coat, 



Escap'' of th^ pnmnkin seedling from tbe seed rnnts, t ^ ^i i J * 



' ' but the lower seed coat 



is caught against this heel, and the twc> arc pulled gradually 

 af)art. In this way the embryo plant pulls itself out from be- 

 tween the seed coats. In the case of seeds which are planted 

 deeply in the soil we do not see this contrivance unless we dig 

 down into the earth. The stem (■! the seedling arches through 

 the sr)il, fjulling the cotvKxlons up at one end. Then it 

 straightens up, the green cot\'ledons part, anil open out their 

 inner faces to the sunlight, as shown in fig. go. If we dig into 

 the Soil we shall see that this same heel is formed on the stem, 

 and that the seed coats are cast off into the soil. 



