HOW THE SEEDLING GROWS FROM THE SEED. 5 



of a seed near the smaller end so that the section will cut across the 

 plumule; sketch showing the positions of the different parts and the relation 

 to the seed coats. 



Exercise 2. 



8. Structure of the bean seed. Take beans which have been soaked in 

 water. Sketch a bean, showing the form, the scar (hilutn) on the concave 

 side, the minute pit (niicropyle) by the side of the hilum. Remove the 

 testa (seed coats) from one of the beans; note the large thick cotyledons; de- 

 termine where the cotyledons are joined (or attached to the young caulicle). 

 Along one side of this point of attachment note the young radicle; at the 

 other end between the cotyledons note the plumule. 



Split open a bean along the line where the cotyledons meet ; sketch one 

 half, showing the young plumule and the venation of the leaf, and at 

 the other side the young radicle. Make a cross-section of a bean and 

 sketch to show the relation of the cotyledons to the seed coats, and the 

 plumule between the cotyledons. 



If there is time, compare a pea seed. 



Exercise 3. 



9. Structure of the grain of corn. Take grains of corn that have been 

 soaked. Note the form, and the difference of the two sides. Sketch a 

 grain of corn showing the depressed area near the smaller end. 



Make a longisection of a grain of corn through the middle line. (If neces- 

 sary make several to obtain one which shows the structures well near the 

 smaller end of the grain.) Sketch the section as shown by one half, observ- 

 ing the following structures : ist, the hard outer " wall " (formed of the con- 

 solidated wall of the ovary with the integuments of the ovules see 

 Chapters 32 and 33) ; 2d, the greater mass of starch and other plant food 

 (the endosperm) in the centre ; 3d, a somewhat crescent-shaped body (the 

 scutellum) lying next the endosperm and near the smaller end of the 

 grain ; 4th, the remaining portion of the young embryo lying between 

 the scutellum and the seed coat in the depression. When good sections 

 are made one can make out the radicle at the smaller end of the seed, 

 and a few successive leaves (the plumule) which lie at the opposite end of 

 the embryo shown by sharply curved parallel lines. Observe the attach- 

 ment of the scutellum to the caulicle at the point of junction of the plumule 

 and the radicle. The scutellum is a part of the embryo and represents a 

 cotyledon. 



Dissect out an embryo from another seed, and compare with that seen in 

 the section. 



