9 8 



ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



of Burdock (Arctium majus, fig. 1088) cling with great tenacity 

 to sheep and other animals. Each burr consists of a number 

 of fruits enclosed by a great many narrow scales, each one of 

 which is bent into a hook at its tip. A 

 different but equally effective arrangement is 

 present in Avens (Geum urbanum, fig. 1088). 

 The group of fruits is not surrounded by 

 clinging scales, but each is provided with a 

 long hook. In some foreign fruits the hold- 

 fasts are of formidable character, and cause 

 much pain to the unfortunate animals which 

 unwillingly promote dispersal. A well-known 

 instance is that of the Harpoon- Plant (Har- 

 pagophytuni) of South Africa, the large fruits 

 of which are covered with stout radiating pro- 

 with Hooks; a few of the hooks, jections provided with powerful hooks. They 



magnified, are shown below J , 



are the source of much inconvenience to such 

 animals as antelopes and lions, being said to sometimes cause 

 the death of the latter. 



Dispersal of Spores by Animals. Fleshy fungi are eaten by 

 various insects that swallow vast numbers of the minute spores 



by which such plants propagate, 

 these passing uninjured through 

 their bodies. In some cases flies 

 are attracted by a sweet fluid (as 

 in Ergot, Claviceps purpurea\ or by 



r^3B ^^ evil-smelling moisture that exudes 



^fPSBiHi H^, on tne spore-producing surface (as 

 ^ in the Stinkhorn, Phallus impudi- 

 cus\ Earth- Worms and other bur- 



ttO doubt help tO 

 of Underground 



fungi, such as truffles. The last- 

 named plants are also eagerly sought and devoured by pigs, with 

 similar results. The dissemination by animals of disease-produc- 

 ing bacteria is too notorious to require emphasizing. 



Fig. 1088. Group of Hooked Fruits of Avens 

 (Geum urbanum) is shown to left, with a single fruit 

 on larger scale. On the right is shown a group of . 

 the Fruits of Burdock (Arctium majus} surrounded disperse tilC 



