174 THE REPRODUCTIVE ORGANS 



lastly the two inner ones, which are the smallest. Alter- 

 nating with these are five stamens, which shed their pollen 

 before the stigma is ripe. These three whorls, unlike the 

 preceding examples, spring from the top of the ovary, 

 and hence are said to be epigynous. The pistil consists 

 of two united carpels inferior to the other whorls. On 

 the top of the ovary is a honey-secreting disk (d), which 

 surrounds the two stigmas, and these ripen only when the 

 pollen of the same flower has been shed. The honey is 

 freely exposed and liable to be spoiled by the rain, and 

 may be obtained by short -tongued insects which commonly 

 visit the flowers. In this case conspicuousness is due to 

 the aggregation of many small flowers at the same level in 

 the inflorescence, and by the outer petals enlarging at the 

 expense of the inner ones. 



The Buttercup, Stock, Strawberry, Rose, Geranium, and 

 Chervil all agree in one important respect their petals are 

 not joined, i.e. the corollas are polypetalous. In most 

 cases the sepals also are free. In the Geranium, however, 

 they are united, and the calyx is gamosepalous. These 

 flowers also show different methods of forming the flower- 

 tube, namely : (a) by erect sepals, as in the Stock ; (b) by 

 a hollow receptacle, as in the Strawberry and the Rose ; and 

 (c) by united sepals, as in the Geranium. 



CHAPTER XIII 



BIOLOGY OF THE FLOWER {Continued) 



II. Pollination of Tubular and Highly Developed Flowers 



The flowers we have considered above are generally 

 simple in structure. Flowers pollinated by the wind have 

 no perianth, or only a very rudimentary one ; they are 

 small and inconspicuous, and produce much pollen ; and 

 the stigmas are large, branched and sticky, to catch the 



