1796 



A TEXTBOOK OF THEORETICAL BOTANY 



of stamens in the centre. Nectar is secreted either at the base of the petals 

 or at the bottom of the calyx. 



Fig. 1690. — Malva sylvestris. Longitudinal sections of flower in three successive stages of 

 anthesis. See in text for pollination mechanism. (After Kniith.) 



In M. sylvestris the red petals are marked with dark stripes which act 

 as nectar guides and above the nectaries are hairs which serve for protection 

 against flies. In the early stage the anthers form a pyramid in the centre 

 of the flower, the filaments being united into a tube below. The immature 

 styles are completely enclosed in this tube so that at an early stage the 

 centre of the flower is entirely filled with ripe anthers. As the latter dehisce 

 they bend outwards and downwards while the stigmas grow up until they 

 occupy the position previously held by the anthers. Insects therefore on 

 visiting a young flower will be liberally dusted with the large, spiny pollen 

 grains, while on visiting an older flower this pollen will be shed on to the 

 stigmatic surfaces. Self-pollination is excluded, for the anthers have bent 

 well out of the way before the stigmas open. The flowers are largely 

 visited by humble bees. 



In M. rotiindifolia the flowers are considerably smaller and are often 

 covered by the large round leaves. In structure they are similar to M. 

 sylvestris but owing to their position they are rarely visited by insects. In 

 this species, therefore, after the anthers have opened, the stigmas grow up 

 but instead of the stamens all bending downwards, they remain more or 

 less erect and the stigmas curl back and ultimately come into contact with 

 the anthers. Miiller suggests that " in the struggle for existence M. 

 rotundifolia has the advantage in being content with poorer soil, in the 

 appearance of its flowers from one to several weeks earlier, and in the 

 possibility of regular self-pollination; M. sylvestris on the other hand, in 

 its more vigorous growth, and much greater attraction for insects". 



