THE ANGIOSPERMAE 



1553 



and the group of small, hard fruits, as a unit. The weight of the fruits 

 causes the structure to fall vvith the fruit lowermost and the bract makes 

 it rotate rapidly. The wind may also carry it further along the ground 

 after falling and the fruits are detached as it goes. The common Hop, 

 Humidus liipiilus, bears a catkin of minute akenes, each with a large papery 

 bract. In the Hornbeam, Carpinus betuliis, the fruits are also borne in a loose 

 catkin and each nut is subtended by a large, leafy and three-lobed bract 

 to which it is firmlv attached. These also rotate in falling and are readily 

 carried for forty or fifty yards or more. 



The habit of spinning in the air seems to offer the advantage of delaying 

 the fall of the fruit. It is beautifully seen in Congea, a verbenaceous climber 

 of southern Asia, in which each cluster of small flowers is surrounded by 

 four spreading, pink bracts. When detached each cluster spins like a 

 propeller in descending. 



Bracts united in an involucre, or rather an involucel, surround each 

 flower of Scabiosa and expand into a papery cup when the fruit is ripening. 

 In some species of the genus this is large enough to act as a parachute for 

 the fruit, sometimes aided by the sepals, which may be plumed or may bear 

 hooked hairs for attachment to animals. The latter is probably the more 



.f^^ 



Fig. 141 5. — Paliurus spina-christi. A, Mature winged fruits. 

 B, Inflorescence. C, Fruit in section. D, Flower. 

 {After Marzocca and Martin.) 



