162 ELEMENTARY STUDIES IN BOTANY 



of the spur. As the moth thrusts its proboscis into the tube, 

 its broad head (against the stigmatic surface) is pressed 

 against the sticky button on each side, so that when it flies 

 away these buttons stick to its head and the pollen masses 

 are torn out. When the next flower is visited, and the head 

 of the moth is pressed against the sticky stigmatic surface, 

 the pollen masses from the previously visited flower are 

 thrust against it and are left there. 



FIG. 129. Flower of figwort (Scrophularia) : A, stigma, in position to receive pollen; 

 B, section of A, showing stamens curved back in tube of corolla ; C, later condition, 

 with style collapsed and stigma not in a condition to receive pollen, but the anthers 

 brought up in position for shedding. After GRAY. 



A very common arrangement to prevent self-pollination 

 in flowers containing both stamens and pistils is for the pollen 

 and the stigma to mature at different times ; that is, when the 

 pollen is being shed, the stigma is not ready to receive ; or 

 when the stigma is ready to receive, the pollen is not ready to 

 be shed. The two following examples will serve to illustrate. 



When the flowers of the ordinary figwort open, the style 

 bearing the stigma at its tip is found protruding from the 

 urn-like flower, while the four stamens are curved down into 

 the tube, and are not ready to shed their pollen (Fig. 129). 

 At some later time, the style bearing the stigma wilts, and the 

 stamens straighten up and protrude from the tube. In this 



