250 



A TEXT-BOOK OF BOTANY 



receptive stigma, and afterward the shedding pollen sacs 

 occupy the same position. A visiting insect will probably 

 find flowers in both conditions; and, while striking against 

 protruding and shedding pollen sacs in some flowers, it 

 strikes against a protruding stigma in other flowers, and 

 thus carries pollen from one to the other. Such flowers 

 are called protogynous , which means "pistil first." 



More frequently, however, flowers are protandrous, 

 which means "stamens first." For example, when the 

 showy flowers of the common fireweed, or great willow herb, 

 first open, the eight shedding stamens project prominently, 

 the style being sharply curved downward and backward, 

 carrying the stigmatic lobes well out of the way (Fig. 245, 

 A). Later, the stamens bend away and the style straightens 



A B 



FIG. 245. Protandr&us flower of willow herb: A, first stage, with anthers in posi- 

 tion for shedding and style curved downward; B, second stage, with anthers 

 past and stigmatic lobes in position for receiving pollen. After GRAY. 



up and exposes the stigma (Fig. 245, B). The result of the 

 visits of an insect is the same as in the case of the pro- 

 togynous flowers. So many cases of protandrous flowers 

 occur among common wild and cultivated plants that 

 illustrations should be discovered easily. 



(3) Difference in pollen. In these cases there are gen- 

 erally two forms of flowers, which differ from each other 

 in the relative lengths of tneir stamens and styles. In 

 the accompanying illustration it will be seen that in one 



