symbiosis. 339 



general, according to the circumstances. Many animals are 



Fig. 379. — Roots of a yellow Gerardia, G, attached to the root of a blueberry bush, B. 

 They enlarge at the points of contact and there send haustoria into the host root. 

 Natural size. — After Gray. 



thus preyed upon by bacteria and fungi. Most communi- 

 cable diseases, such as typhoid fever, diphtheria, and tuber- 



B A 



Fig. 380. — A , European dodder twining about a hop stem. All but the uppermost coils 

 show the groups of wartlike swellings from which haustoria penetrate the host stem. 

 Natural size. B, Germination of same. The various stages are arranged in order 

 from right to left. In the last stage the seedling has found a suitable support and has 

 absorbed all the reserve food in the thickened lower end, which has withered and died, 

 freeing the plant from the ground. Magnified about 2 diam. — After Kerner. 



