THE STAMEN AND POLLEN-SAC 



245 



by the protection which they give to the inner parts of the young bud ; 

 the petals by giving scent, and a wide expanse of coloured surface, by 

 which means the flower is made attractive. Both parts are subject in 

 special cases to modification of form and character in relation to pollina- 

 tion; but these details must be left aside for the present. 

 After the flower is full blown, the petals wither and 

 fall away. The sepals frequently fall away also, as in 

 Crucifers and in the Buttercup. Sometimes they 

 drop even before the flower is full blown, as in the 

 Poppy. In other cases they persist, as in the Rose, 

 Violet, or Pea, though their further use is not obvious. 

 The stamens which lie within are essential for pro- 

 pagation. Their function is to produce pollen-grains 

 which, after further development, give rise each of 

 them to two male fertilising cells, or gametes. The 

 form and structure of the stamens may vary in detail 

 in special cases. But in the great majority of flowers 

 they conform to one simple type, consisting of a cylin- 

 drical stalk or filament, which is continued upwards 

 into the distal anther (Fig. 191). This is two-lobed, 

 the lobes being attached laterally along the filament. While young the 

 outer surface of the anther is turgid, and unbroken. When ripe it 

 opens, sometimes by pores, as in Solanum, but usually by longitudinal 

 slits, right and left, which gape widely, as in Iris or Caltha. Thus the 

 pollen is shed as grains, usually separate and of yellow colour. The 

 ripening of the stamens coincides with the blooming of the flower ; 

 but in cases where the stamens are numerous they may open in 



FIG. 191. 

 Stamens of Iris : 

 that on the right 

 shows dehiscence. 

 (After Figuier.) 



A />' 



FIG. 192. 



Sections of the anther of Caltha. A, before dehiscence, showing the four pollen 

 sacs still closed. B, after dehiscence, showing the sacs open, and the slits gaping 

 widely. (Enlarged.) F. O. B. 



succession, so that the shedding of the pollen may be spread over a 

 lengthened period. After the pollen is shed the stamens usually fall 

 away, or sometimes they persist in a withered state ; but they serve 

 no further function. 



If the anther of any ordinary stamen be cut transversely it is found 



