THE ANGIOSPERMAE 1563 



twigs and shoots, with fruits attached, may be carried about by animals or 

 birds, as for example in Galium oparine, and Cerastium tetrandrum. The 

 same thing is observed in other parts of the world, and Opuntia in Australia, 

 Forskohlea in the Mediterranean region and Pemphis acidiila on oceanic 

 islands {e.g., Cocos-Keeling) are easily disarticulated and carried about in 



this way. 



Sometimes plant organs may provide means of attachment instead of 

 hairs. The styles in some species of Geum (G. iirbamim, G. rivale) are per- 

 sistent and are sharply deflexed below the stigma. The hook so formed 

 becomes woody and sharp after the stigma and upper portion of the style 

 have been detached, and provides a very effective attachment. The 

 arctic and montane species of Geum have long plumed styles like those 

 of Clematis and are wind-distributed, which may be associated with the 

 absence of large mammals in their environments. Many species of Ranun- 

 culus also have sharply curved, though short styles {R. acris, R. hulbosus) 

 which often attach the akenes to woolly clothes. The genus Bidens takes 

 its name and owes its dispersal to the two (sometimes three or four) calyx 

 segments which constitute the pappus and take the form of stiff spines 

 with barbed, reflexed bristles by means of which the fruits are pulled 

 oft" and transported. The widespread southern genus Acaena (Rosaceae) 

 is similarly equipped, the sepals either ending in sharp points or bearing 

 hooked spikes which are persistently adherent. The inner sepals of Rumex 

 are persistent and in some species are furnished with sharp spiny edges 

 by means of which the fruits adhere to animals. Another genus of Poly- 

 gonaceae, Emex (Fig. 1424), has also spiny sepals, but only one spine on 

 each of the three persistent sepals. They are hard and sharp, but are not 



V 



Fig. 1424. — Emex aiist rails ( Polygonaceae). Spines on three of the persistent perianth 



leaves 



