FRUITS AND SEEDS 197 



stroyed, but some are carried away and dropped, others 

 stored in holes and forgotten. 



(b) Adhesive fruits and seeds become attached to the 

 hairy coats of animals, and may be carried considerable 

 distances before they are finally dropped or rubbed off. 

 In burdock the achenes are smooth, but the involucral 

 bracts enclosing the head are hooked ; the fruits of 

 cleavers (Galium Aparine) and enchanter's - nightshade 

 (Circcea lutetiana) are covered with short stiff bristles ; 

 the achenes of avens (Geum) are hooked (Fig. 106). In 

 Bidens (the bur-marigold), the achenes are armed with 

 barbed prongs (Fig. 107) ; in agrimony the receptacle is 

 covered on the outside with hooked bristles. 



5. Water-Borne Fruits and Seeds. Aquatics which 

 flower and fruit under water must obviously have their 



FIG. 105. DEHISCED FIG. 106. ACHENE OF FIG. 107. ACHENE 



CAPSULE OP VIOLET. AVENS (Geum}, WITH (CYPSELA) OF BUB- 



HOOKED STYLE. MARIGOLD (Bidens}. 



seeds dispersed by water. Seeds dropped into water 

 may float and be carried some distance and washed up on 

 land. Dry fruits often contain a considerable amount of 

 enclosed air. If such fruits fall into water, they float and 

 may be driven along the surface of the water by the wind. 

 In this case the agent of distribution is the wind, not the 

 water. Few special structures for water- dispersal are 

 found among English fruits. In the white water-lily, 

 however, the fruit is a large berry, containing a large 

 number of seeds. Each seed is surrounded by a spongy 

 aril, containing cavities filled with air. When the fruit 

 opens, the seeds float up to the surface of the water, 

 and are drifted about until the aril rots, when they sink. 

 In fresh water seeds may germinate while floating on the 

 surface e.g., willowherb. If driven ashore by the wind, 

 they may continue to live. 



