132 THE BOOK OF NATURE STUDY 



stalks. Each stamen stands opposite the middle line of a petal. 

 The anthers open inwards, and expose the sticky yellow pollen. 



In the centre of the flower, occupying the summit of the floral 

 receptacle, is the pistil. This consists of a pale green, globular 

 ovary, a long slender style like the shaft of a pin, and a small ex- 

 panded stigma like the head of a pin. In the long-styled flowers 

 the style is about the length of the tubular part of the corolla, 

 and the stigma stands at the entrance to the tube. The surface 

 of the stigma will be seen with a lens to be distinctly papillate and 

 rough. When the ovary is carefully opened or cut through longi- 

 tudinally, the numerous, small, greenish white ovules will be 

 found to be borne on a globular projection from the base of the 

 cavity. There is no trace of partitions dividing the latter, and 

 only comparison with the other parts of the flower shows us that 

 the pistil is composed of five carpels very completely united 

 together. 



The short-styled or thrum-eyed flowers are composed of the 

 same parts as the long-styled, but the widening of the corolla tube 

 will be found not about the middle but close to the upper end. 

 The stamens are attached here so that their anthers project in the 

 entrance to the corolla. The style, on the other hand, is much 

 shorter in these flowers, and the stigma stands about half-way 

 up the tube, i.e. at about the same level as the anthers in the 

 long-styled flowers. The stigma is smoother and the pollen 

 grains are larger in the short-styled flowers. 



This remarkable development of two types of flower, both con- 

 taining stamens and pistil but the position of the stamens in the 

 one flower corresponding to that of the stigma in the other, occurs 

 in a number of plants, the Primrose and its relations being the 

 most familiar examples. In the Primrose it has been found that 

 the best production of seed results when pollen is carried from 

 stamens standing at the same level as the stigma receiving the 

 pollen. This can only be brought about by a transfer of pollen 

 from one type of flower to the other, that is, by cross-pollination. 



While flowers may sometimes be self-fertilised, it has been 

 found, by carefully watching the plants when in flower, that on 

 favourable days a number of insects of different kinds visit the 

 flowers in search of the nectar secreted at the base of the ovary. 



