4/8 THE BEAN PLANT. [CHAP. 



jS. By making careful transverse sections of young 

 flower buds the stages of development of the anther 

 and pollen may be made out. Observe especially 

 the origin of the pollen-grains by the successive 

 division of each of the numerous mother-cells, into 

 two and then into four. Each of the four daughter- 

 cells forms a wall of its own and becomes a 

 pollen-grain. 



5. The pistil, 



a. It is found by tearing open the stamen-tube : it 

 is a long green tapering body, somewhat flattened 

 laterally and ending in a point (the style) which 

 bears a tuft of strong hairs. 



b. Slit it open carefully: its central cavity contains 

 a number of small oval bodies, the ovules^ attached 

 along its ventral side by short pedicles. 



c. It is difflcult to get a section of a bean-ovule, 

 but its essential structure may be readily made 

 out by making thin transverse sections of the 

 ovary of a large lily (where the ovules are closely 

 surrounded by the tissue of the pistil) and examin- 

 ing with I inch obj. 



a. The central cellular portion of the ovule {nucel- 

 lus) made up of a large number of cells. 



p. Its two coats, an inner (J>ri7?iine) and outer 

 {secundine). 



y. The small passage {micropyle) leading through 

 the coats down to the nucellus. 



8. In median sections of the ovule, a very large 

 cell (the embryo-sac) will be seen in the -nucellus 

 just opposite the micropyle. 



