406 



TREES AND SHRUBS. 



growth is usually continued by one of the uppermost side 

 buds. 



The flowering branches (Fig. 172), whose buds are much 

 larger than the ordinary buds, resemble those of Sycamore in 

 general structure, but are erect ; they open in April or May, 

 as a rule, sometimes not until June. The thick erect axis 

 bears clusters of flowers below, single flowers at the top. 

 Each cluster contains (1) male flowers, with stamens but no 

 pistil ; (2) complete flowers, of which some are really female, 

 since the stamens fall off before the anthers open ; (3) flower- 

 buds, which do not open but wither and fall off. 



Each flower is stalked, stands out horizontally, and is 

 irregular (zygomorphic) ; there are five united green sepals 



forming a bell-shaped calyx, 

 four free petals (an upper 

 pair and a lower pair, some- 

 times with a fifth odd petal 

 below) . Each petal is white, 

 with a yellow blotch (larger 

 in the two upper petals) 

 which later turns red, and 

 jagged edges. Within the 

 petals there is a ring-like 

 nectary, thickest at the upper 

 side of the flower, and with- 

 in this the stamens (usually 

 seven) are inserted. Each 

 stamen has a long filament 

 which turns up at the end 

 and bears a red anther. The 

 pistil has a three-chambered ovary and a long pointed style 

 bearing stigmatic hairs. 



The flowers are visited by insects, especially bees. In a 

 perfect flower the style is ready to receive pollen before the 

 anthers open. When a bee visits a newly opened flower the 

 style, which projects forwards and upwards, touches the bee's 

 abdomen, while the unripe stamens are bent down. Later 

 the stamens ripen and turn forwards and upwards, so that 

 the anthers are brought into the position formerly occupied 

 by the style. Cross-pollination is further aided by the fact 

 that the male flowers in an inflorescence are the first to open, 



Fig. 172. Flowering Branch of Horse 

 Chestnut. 



