260 FRUITS AND SEEDS. 



animals carry the seeds off intentionally to their nests, and 

 often drop them by the way, as squirrels do with acorns, 

 for instance ; ants play an important part in seed distribu- 

 tion in this way. 



(1) Many fruits possess hooks, and hence may adhere to 

 the wool or fur of passing animals. These adhesive con- 

 trivances are usually outgrowths of the fruit and not of the 

 seed. Examples are afforded by Avens (hook = persistent 

 style on each akene) ; Corn Buttercup ; G-oosegrass ; Wood- 

 ruff ; Medick (pod coiled, bearing hooks) ; Hound's-tongue ; 

 Sanicle, Carrot, Chervils, and a few other Umbellifers; 

 Agrimony (hooks on receptacle) ; Enchanter's Nightshade 

 (Fig. 87). The flower-heads of Teasel and Burdock have 

 hooked bracts so that a passing animal may catch the plant 

 and drag it forward, the rebound causing the fruits to be 

 jerked out ; or, in Burdock, whole burs (fruit-heads) may 

 thus catch on to the animal and be carried off. 



In Burweed (Xanthium, a curious Composite, found in 

 South England but not native, with small heads of unisexual 

 flowers) the female flower-head is covered with hooked 

 prickles and ends in two short conical beaks ; and in Bur- 

 marigold (Bidens') each akene has a pappus of two or three 

 stiff bristles covered with small downward-pointing prickles. 

 The most formidable hooked fruits occur in tropical plants 

 such as Martynia and Harpagophytum, which are usually 

 shown in botanical museums. Hooks and spines also serve 

 to protect fruits against animals which might otherwise eat 

 them ; this is probably the case with the spiny capsules of 

 Horse Chestnut, the stiff bristles (awns) of Barley, etc. 



(2) Active dispersal takes place when animals seek out 

 fleshy fruits in order to devour them. The seeds are protected 

 by hard stones in the case of drupes, or by thick leathery seed- 

 coats in the case of most berries, by the pericarp in fruits 

 such as those of the Strawberry or the Eose. In most cases 

 the covering of the seed is hard and quite indigestible, and in 

 not a few cases the seed itself is poisonous. Hence in many 

 cases the seed can pass through the animal's body without 

 being injured, and if deposited in suitable soil may succeed 

 in germinating. Very often, however, the hard part of the 

 fruit is never swallowed, but allowed to fall to the ground 

 after the soft part has been pecked ; for the animals concerned 



