THE ANGIOSPERMAE 



1319 



large, apical, stigmatic surface. Since it only begins to grow after the last 

 anther has withered, dichogamy is complete. Insects visiting the young 

 flower must be dusted with pollen, while those working in an older flower 

 will discharge their pollen on the newly grown stigma. Automatic self- 

 pollination is impossible, but occasionally the style of one flower may touch 

 the anthers of an adjacent one. 



Fig. 1236. — Scabiosa arvensis. A, Capitulum. B, Marginal flower. 

 C, Disc flower. D, Vertical section of flower in first, male state. 

 E, The same in later, female state. 



From time to time examples of gynodioecism have been recorded in this 

 flower. In some parts of the country plants have been observed in which all 

 the flowers were female, while nearby, typical hermaphrodite plants could 

 be found. Indeed, in many plants the florets of some inflorescences exhibit 

 incomplete hermaphroditism, the stamens being much reduced and pro- 

 ducing no pollen. Such heads are often smaller than the fully herma- 

 phrodite ones and are often produced early in the year. 



Scabiosa arvensis appears to be pollinated almost entirely by a single 

 species of bee, Andrena hattorfiana, which rarely visits any other flower, and 

 it is probable that the plant and the bee have a common geographical distri- 

 bution, though the details have not been worked out. On the other hand 

 this bee is not the only insect visitor to the plant, though other visitors are 

 rare and doubtfully efl'ective as pollinators. 



