206 PRACTICAL COURSE IN BOTANY 



Remove the perianth and sketch the remaining organs in 

 profile, showing the position of the stamens. Do you see 

 any advantage in their position? Can you determine the 

 use of the crest of hairlike filaments on the upper side of the 

 sepals ? Remove a stamen and sketch it. 



223. The pistil. Remove as much of the upper part of 

 the perianth tube as you can without injuring the pistil, 

 and with a sharp knife cut a vertical section down through 

 the ovary so as to show the long style and its connection with 

 the placenta. Make a sketch of this longitudinal section 

 (see Fig. 291), labeling the parts observed. Notice whether 

 the placenta is central or parietal. Draw a cross section of 

 the ovary ; how many locules has it ? How many ovules in 

 each? Where are they attached? Is the placenta free 

 central or axial (Fig. 293) ? Examine with a lens the little 

 flap at the base of the two-cleft apex of one of the stigmas, and 

 look for a moist spot to which the pollen will adhere. Label 

 this in your sketch, stigmatic surface. No seeds can be ma- 

 tured unless some of the pollen reaches this surface ; can you 

 think by what agency it is carried there? What insects 

 have you seen hovering about the iris? Notice that in 

 drawing his head out of the flower, an insect would not 

 touch the stigmatic surface, since it is on the upper side of 

 the flap and he would be probing under it. But in entering 

 the next flower that he visits, he is likely to 

 strike his head against the flap and turn it 

 under, thus dusting it with pollen brought 

 from another flower. 



224. Diagrams. -- Draw diagrams show- 

 ing the horizontal and vertical arrangement 

 FIG. 294. Hon- of parts in the iris or other specimen ex- 

 flower. dlagra amined, and compare with those made of 



the monocotyl studied in the preceding sec- 

 tion. In what respect does it differ from them? How do 

 you account for the difference in the number of stamens, if 

 there is any? (220.) 



