204 



OUTLINES OF PLANT LIFE. 



ovoid, or even angular, with the surface smooth, grooved, or 

 roughened with few or many bosses, points, or ridges, as in 

 other spores (A-D, fig. i66). They are either dry and 

 powdery when the sporangia burst, or are moist and sticky. 



Fig. 163. Fig. 164. Fig. 165. 



Fig. 163. — Anther and pollen of a Rhododendron. A, the anther, opening by pores at 

 the end and allowing the pollen to escape. Magnified 8 diam. B^ pollen grains ad- 

 herent in fours (tetrads) as formed in the mother cells ; the tetrads are held togetlier 

 by a sticky material which draws out into cobwebby threads as they are separated. 

 Magnified 50 diam. — After Kerner. 



Fig. 164. — Anther of the sweet violet {Viola odorata), showing the pollen sacs opening 

 by slits. Magnified about 5 diam. — After Kerner. 



Fig. 165. — A flower of cinnamon, halved. The calyx and stamens are raised on a cup 

 developed around the pistil. The anthers open by uplifted valves, one for each spo- 

 rangium, which here are arranged in two stories instead of in pairs side by side. Mag- 

 nified about 7 diam. — After Luerssen. 



adhering to each other in larger or smaller clusters (fig. 163). 

 Sometimes, as in orchids and milkweeds, they are all held 

 together in one mass and are attached to a part of the anther 

 which carries the mass like a stalk or handle (fig. 167). Dry 

 spores are usually adapted to distribution by wind ; while the 

 coherent spores are adapted to carriage by small animals, 

 especially insects. (See further \ 295.) 



