Simple Plants Without Chlorophyll — Fungi 111 



trees, in which the leaves curl and become yellow. Single asci are formed 

 on the surface of the diseased leaves. The disease may be prevented by 

 a thorough application of a ''dormant spray" (Bordeaux mixture and 

 lime sulfur sprays) two weeks before the buds unfold. The economic 

 importance of yeasts is considered in the chapter on Economic Impor- 

 tance of Plants. 



5. Mildews (mil' du) (A.S. mildeaw, honeydew). — Powdery mildews 

 are fungi which are chiefly parasites on the leaves and stems of flowering 

 plants. The masses of hyphae appear as whitish, or grayish, powdery 

 areas on the surfaces of the aff'ected plant. Certain hyphae, the haustoria 

 (hos-to'ria) (L. haurire, to drink) penetrate and absorb food from the 

 cells of the plant host. Asexual reproduction occurs by forming chains 

 of spores (conidia) at the tips of the surface hyphae. 



Ascospores are formed within the asci. The asci develop within small, 

 closed ascocarps, known specifically as cleistothecia or perithecia (kli sto- 

 the'sia) (Gr. kleistos, closed; theke, box) (peri -the' si a) (Gr. peri, 

 around; theke, box) . The latter are produced by the hyphae on the sur- 

 face of the host plant. Sometimes the hyphae of the asocarp may be 

 elongated and delicately branched. 



Powdery mildews appear as whitish, dusty patches upon such plants 

 as lilacs, roses, apples, clovers, dandelions, grapes, maples, berries, and 

 other flowering plants. Dusting infected plants with flowers of sulfur 

 may be beneficial in combating these diseases. 



6. Blights (blite) (A.S. hlaecan, grow pale).- — Blights are diseases of 

 plants in which the blossoms, young leaves, or branches die suddenly. 

 Examples are the fire blight of pears and the blight of chestnut trees. 

 The latter is produced by the ascomycetous fungus (Endothia parasitica) 

 which was introduced from China about 1900 and which has killed most 

 of the chestnut trees in the United States. In these the asci are present 

 in dark, ovoid ascocarps known specifically as perithecia. Conidia 

 (spores) may be produced in flask-shaped fruiting bodies called pycnidia 

 (pik-nid'ia) (Gr. pyknos, dense; idium, diminutive). The mycelium 

 of the fungus parasitizes the cambium and the living cortex cells of the 

 chestnut tree. 



C. Class Basidiomycetes (ba sid io my -se' tez) (Gr. basis, base or club; 



mykes, fungus) 



1. Mushrooms. — Mushrooms are saprophytic fungi which derive their 

 foods from decomposing organic materials in the soil, dead leaves, bark, 



