214 THE BOOK OF NATURE STUDY 



the same parts as in the Charlock or Lady's Smock. It is therefore 

 unnecessary to describe the arrangement of the parts in detail. 

 There are two pairs of sepals, four small white petals, two short 

 stamens and two pairs of longer stamens, and the pistil. Since 

 the anthers of the longer stamens stand at about the level of the 

 stigma, pollen will easily get upon this, and the flower be self- 

 pollinated. Nectar is, however, secreted by a pair of nectaries at 

 the base of each of the shorter stamens and, when the flower is 

 visited by insects, cross-pollination may be effected. The flower 

 is thus of interest in being constructed on the plan of an insect- 

 pollinated flower, but relatively reduced and inconspicuous and 

 mainly dependent on self-pollination. 



The pistil, composed of two carpels, is short and flattened, and 

 extended in the plane of the shorter stamens 

 in the flower. It consists of the ovary, a 

 short style, and a rough two-lobed stigma. 

 The fruit (Fig. 97) is derived from the pistil, 

 the other parts of the flower falling away. It 

 is flattened, and widens gradually from below 

 FIG. 97. Fruit of the upwards. At the broad upper end is a de- 

 Shepherd's Purse pression, from the middle of which the remains 



opening to liberate f ^ ^ projects. The fruit Consists of 



the seeds. (After 



Baiiion.) two chambers separated by a partition which 



lies in the plane at right angles to that of the 

 flattened pod. The greater part of each of the carpels can be 

 pulled away, leaving the seeds attached to the margin of the 

 septum. What can be done artificially happens naturally when 

 the fruit is mature (Fig. 97), and in this way the seeds become free. 

 In its construction the pistil and fruit of the Shepherd's Purse 

 thus resembles that of the Charlock (p. 212), although it is short and 

 broad instead of elongated. Owing to the certainty of pollination, 

 every flower produces a fruit, and the large number of seeds pro- 

 duced explains the abundance of the plant in suitable situations. 



THE COMMON AVENS (Geum urbanum, L.). 



The Common Avens is a perennial herb growing by roadsides 

 and often in the shade of woods, and flowering from June to 



