CHAPTEE III 



MOVEMENTS, DEVELOPMENT, AND MORPHOLOGY OF THE 



SEEDLING 



14.' How the seedling breaks ground. 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, sends a tightly rolled, pointed leaf 

 vertically upward into the air ; but seedlings 

 in general are not found to do 

 anything of the sort. The squash 

 seedling is a good one in which 



A D c D E 



FIG. 8. Successive stages in the life history of the squash seedling 



GG, the surface of the ground ; r, primary root ; r', secondary root ; c, hypocotyl ; 

 a, arch of hypocotyl ; co, cotyledons 



to study what may be called the arched 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. 8. 



The seed is gradually tilted until, at the time of their emer- 

 gence from the ground (at C), the cotyledons are almost ver- 

 tical The only part above the ground line GG ? at this period, 



