374 TEXTBOOK OF BOTANY 



c. Alga-like Fungi. These possess many characteristics in 

 growth and reproduction which indicate that they may 

 have arisen from the algae. The bread mold and its 

 relatives are among the members of this group. Some 

 of the parasitic iorras are discussed in §§ 382-384. 



d. Sac Fungi. These produce usually at least two types 

 of spores ; those of one type are produced on thread- 

 like projections from the plant body; spores of a 

 second sort are borne in small sac-like structures which 

 most commonly contain eight spores, but in some 

 species contain more or fewer than eight. The sacs 

 are in most cases partly or entirely surrounded by in- 

 terlacing branches of the fungus, which form a fruiting 

 body of characteristic form. (See §§ 385-389.) 



e. Basidium Fungi. The mushroom and its relatives 

 belong to this group, in which the rusts and the smuts 

 (§ 390) .are usually included. 



/. Imperfect Fungi. To this group belong a large num- 

 ber of disease-producing fungi. They are called " im- 

 perfect " because it is believed by most students of 

 fungi that we do not know their entire life history. 

 Many formerly listed in this group have been found, 

 when their whole history was worked out, to be sac 

 fungi ; others have been referred to the basidium fungi. 

 (See§§ 391-393-) 

 379'. Pear Blight. — This disease, known also as " fire 

 blight " and " twig blight," is probably the most important 

 bacterial disease affecting cultivated plants. It attacks the 

 apple, crab-apple, pear, quince, and some related plants. 

 The ravages of the disease are so serious that the growing of 

 pears and apples has been almost entirely given up in some 

 regions of the United States. The bacteria that cause it 

 live in the inner tissues of the twigs and branches. The 

 first symptom that is likely to be noted is a withering of the 

 leaves, flowers, and younger branches in from two to four 



