200 



PRACTICAL COURSE IN BOTANY 



or of the lobes of the ovary. Examine the tip with a lens 

 and notice the sticky, mucilaginous exudation that moistens 

 it. Can you think of any use for this ? If not, tou(!h one of 

 the powdery anthers to it, and examine it again with a lens. 

 What do you see? Can you blow or dust the pollen from 

 the stigma? 



215. Pollination, or the transfer of pollen from the anther 

 to the stigma, is a matter of great importance, as the pistil 

 cannot develop seed without it, except in the case of a few 

 plants like the Alpine everlasting, some species of meadow 

 rue {Thalidrum), and Alchemilla, which have the unusual 

 faculty of perfecting seeds in the absence of pollen. Note 

 the relative position of pistils and stamens and see if it is 

 such that the pollen can reach the stigma without external 

 agency. 



216. The ovary. — Observe the shape of the ovary, and 

 the number of ridges, or grooves, that divide the surface. 



Select a flower which has begun to 

 wither, so that the ovary is well 

 developed, cut a cross section near 

 the middle, and try to make out the 

 number of locules, or internal divi- 

 sions. Do you perceive any corre- 

 spondence in number between these 

 and the ridges or lobes outside (Fig. 

 280) ? Between them and the lobes 

 of the stigma? The walls that 

 inclose the cavities of the ovary 

 are called carpels, and the ridges or 

 depressions that mark their point 

 of union on the outside are the 

 sutures, or seams. The little round 

 bodies in the locules, as the compartments of the ovary are 

 called, are the ovules, which will later be developed into seeds. 

 Their place of attachment is the placenta. If they are 

 attached to the walls of the carpels (Fig. 281), the placenta 



-^ r 



279 280 



Figs. 279, 280. — Ovarj- of 

 yucca, a hypogynous mono- 

 cotyl, dissected : 279, vertical 

 section ; oz;, ovules ; 280, diagram 

 of a horizontal section of the 

 same, enlarged, showing the 

 three carpels and six locules ; 

 ds, dorsal sutures ; vs, ventral 

 sutures ; ov, ovules ; pi, pla- 

 centa. 



