92 



DEPENDENT PLANTS 



134. The cultivated mushroom, a saprophytic plant. 



fungus is called mycelium. Some of the hyphse finally grow 

 out of the leaf and produce spores or reproductive cells 



which answer the 

 purpose of seeds 

 in distributing the 

 plant (6, Fig. 137). 

 195. The ab- 

 normal condition 

 produced in plants 

 by fungous and 

 bacterial parasites 

 and by other agents 

 is known as a dis- 

 ease. On some 

 plants, the disease takes the form of a leaf -spot or a blight; 

 in others swellings or galls are produced. Cankers on branches 

 of trees and on stems of herbaceous plants are produced 

 by fungi living in the affected tissue. The well-known fire- 

 blight and blight-canker 

 of pears are caused by 

 bacteria. The rots of 

 fruits and vegetables 

 are largely produced by 

 fungi or bacteria. 



196. Some parasites 

 spring from the ground 

 (Figs. 131, 132), as 

 other plants do, but 

 they are parasitic on 

 the roots of their hosts. 

 Some parasites may be 

 partially parasitic and partially saprophytic. Many (perhaps 

 most) of these root-saprophytes are aided in securing their 

 food by soil fungi, which spread their delicate threads over 

 the root-like branches of the plant and act as intermediaries 



135. Saprophytic fungus. One of the shelf fungi 

 (Polyporus) growing on dead trunks and logs. 



