234 



BOTANY OF THE LIVING PLANT 



the larger supply of pollen thus provided to meet the risks of failure in 

 pollination. 



In " doubled " flowers similar features of pleiomery are seen. " Doubling " 

 often consists merely in a petaloid development of stamens ; and it most 

 commonly occurs in flowers with an indefinite number of stamens. But it 

 often involves also an actual increase in number of the petaloid parts, effected 

 by methods of fission, as well as of interpolation of extra whorls, or of extra 

 mdividual parts. 



(v) By Meiomery is meant that the number of parts of one category 

 stands below the fundamental number for the whole flower. It is 



Fig. 183. 

 Flower of Scrophularia nodosa, which is pentamerous. The five stamens are 

 represented, but the posterior stamen (si') has no anther : it is merely a vestigial 

 staminode which marks the place of a normal stamen. 



most often seen in the gynoecium ; but it appears also in the androe- 

 cium, especially in flowers where the mechanism is highly specialised. 

 It occurs less frequently in the outer floral parts. In the gynoecium 

 it may be referred to a fading out of the activity of the floral shoot, 

 or even a deficiency of room for the full number of parts. The result 

 is that the carpels are frequently fewer than the other parts. For 

 instance, in the Compositae, the Umbelliferae, and most Gamopetals 

 there are only two carpels in the pentamerous flower. But in many 

 cases it is clear that the smaller number is the result of abortion of 



:J 



