14 SEEDS AND SEEDLINGS 



The first evidence of germination in the corn (Fig. 4) is 

 the emergence of the root sheath enclosing the root which soon 

 pushes through at the tip. This is quickly followed by the 

 formation of side roots which really arise from the stem. Imme- 

 diately following the emergence of the root sheath, the coni- 

 cally rolled leaves (plumule) push out from the opposite end 

 of the groove and grow upward. The single cotyledon acts as 

 an organ of absorption, the same as in the castor oil seed but 

 does not rise above the surface of the soil and take on foliage 

 characteristics. 



The primary root elongates rapidly and produces an abun- 

 dance of minute root-hairs (Pages 25 and 26), which serve for 

 the absorption of water and nutriment from the soil. The stem 

 elongates and new leaves are produced. 



We have seen that the cotyledons serve different functions 

 in different seeds; i.e., for storage, for absorption and for fol- 

 iage. A careful study of the characters of the seeds of a large 

 number of plants and their germination will prove both instruc- 

 tive and interesting. 



EXERCISES WITH SEEDS AND SEEDLINGS 



1. Take a few dry beans and a few that have been soaked in water 

 for three or four hours. Note the shape, the point of attachment (hilum) 

 and the small opening or micropyle near it. Remove the seed coats and 

 note their horny character. Note the two large cotyledons; they are con- 

 nected by the short radicle which gives rise to the first root and the first 

 stem or hypocotyl. Note the plumule or first bud lying between the two 

 cotyledons, just above and attached to the radicle. Make drawings or 

 diagrams, to show all these points. 



2. Castor Bean Seeds.^Examine a few castor beans and compare with 

 the beans. Note the thick bodies (caruncles) at point of attachment. Re- 

 move the seed coats. Make a careful examination and locate the embryo. 

 Compare the cotyledons with those of the bean and note that they are thin 

 and leaf-like. Note the character of the surrounding material. In what 

 way is this seed like the bean? How is it different? Make drawings or 

 diagrams and label the parts. 



