162 



ESSENTIALS OP BOTANY 



merely a prolongation of the filament. Within each lobe 

 are two pollen-sacs filled with mother cells from which 

 the pollen grains are developed, each cell usually pro- 

 ducing four pollen grains. 

 After the anther has ma- 

 tured, the two sacs of each 

 lobe commonly run together 

 into one cavity, which is only 

 partially filled with pollen 

 grains. The shape of the 

 anther and the way in which 

 it opens depend largely upon 

 the way in which the pollen 

 is to be discharged and how 

 it is carried from flower to 

 flower. The commonest 

 method is to have the anther- 

 cells split lengthwise, as in 

 Fig. 119, 1. A few anthers open by trap-doors like valves, 

 as in II, and a larger number by little holes at the top, as 

 in III. 



Sometimes the anthers face outward and open outward, 

 as in the wild ginger (Fig. 98); but more frequently they 

 face and open inward, as in the thistle, the pond lily, and 

 the primrose (Figs. 109, 115, and 134). 



The pollen in many plants with inconspicuous flowers, 

 as the evergreen cone-bearing trees, the grasses, rushes, 

 and sedges, is a fine, dry powder. Powdery pollen is 

 adapted to be carried by the wind. In plants with showy 

 flowers the pollen is often somewhat sticky or pasty. 

 Sometimes pollen grains of this kind are bound together 

 in small masses by fine, cobweb-like threads, as in tlie 

 Milkweed Family (Asclepiadacecc). 



Fig. 119. Modes of discharging 

 Pollen. 

 I, by longitudinal slits in the anther- 

 cells (amaryllis) ; II, hy uplifted 

 valves (barberry) ; III, by a pore 

 at the top of each anther-lobe 

 (nightshade) . 



