128 THE BOOK OF NATURE STUDY 



to its being approached by the insect in a particular way, the 

 converging lines on the petals pointing to the entrance to the 

 nectary, the hairs on the lateral petals limiting the entrance to 

 below the stamens, and the deeply seated nectar all find their 

 explanation in the light of a knowledge of the pollination of the 

 flower. The arrangement of the stamens and stigma deter- 

 mine the special mechanism for shedding and receiving the pollen. 

 Only the first developed flowers of the Sweet Violet have the 

 structure described above. A little later in the season, when the 

 new rosette of leaves is unfolding on the plant, the flower buds 

 give rise to small and inconspicuous flowers, which remain hidden 

 among the leaves and do not open. These flowers are self-polli- 

 nated, the pollen from the stamens reaching the stigma, around 

 which the anthers are placed. These flowers 

 are thus always fertilised and set fruit, while 

 the conspicuous flowers must be cross-pollinated 

 by means of insects for this to take place. 



The fruit of the Violet, whether developed 

 from the large or the inconspicuous flowers, is 

 formed from the pistil. The sepals persist 

 FIG 6; Wild Pans aroun d the base of the fruit, but the petals 

 (Viola tricolor), and stamens wither and fall off (as does the 

 Fruit opening by style) as the ovary enlarges. The fruit contains 



vaivel^ int threC a number of smooth round seeds attached in 

 three rows to the inside of the wall of the 

 developed ovary. As the fruit ripens its wall becomes dry, and 

 ultimately splits into three valves along lines midway between 

 the rows of seeds. As the valves of the fruit dry their edges curl 

 inwards. In the Sweet Violet this serves merely to loosen the 

 attachment of the seeds, which fall off ; but in other species, such 

 as the Wild Pansy (Fig. 65), the seeds are thrown to some distance 

 from the fruit. The smooth seeds are nipped by the infolding 

 edges of the valve, and are jerked away, just as a smooth marble 

 might be if nipped by the finger and thumb. 



The Dog Violet will be found to resemble the Sweet Violet 

 in many respects, and, like it, has both conspicuous and self- 

 pollinated flowers which do not open. The Wild Pansy, on the 

 other hand, has only conspicuous, insect-pollinated flowers. The 



