DISEASES CAUSED BY FUNGI 19 



rule doing appreciable damage ; Puccinia Cannes (Wint.) Henn., 

 common on garden cannas ; Uredo Arachidis Lag., common on 

 ground-nut and sometimes destructive ; Cerotelium (Kuehneola) 

 Gossypii (Lag.) Arth., common and sometimes severe on some 

 perennial cottons, but not very often seen on Sea Island types. 

 The bright yellow Uredo form of Phakopsora vitis Syd. is generally 

 common on grape vines, and a brown Uredo on Dolichos ; the 

 pigeon pea is frequently seen in Trinidad with leaves rusted by 

 Uromyces Dolicholi, Arth. 



Rust infestations may be kept down by spraying with 

 Bordeaux mixture (see ground-nuts) and resistant varieties have 

 been found in several important cases. 



The Smuts : Ustilaginales. 



The smut fungi are somewhat nearly related to the rusts, 

 though very different in their general habit. Like the rusts, 

 they are strictly parasitic, depending for nourishment on living 

 plants. They attack plants of widely different orders, perennials 

 as well as annuals ; their economic effects being most serious on 

 the cereal crops. They are few in number and of very small 

 importance in the West Indies. 



Typically the host is infected in the seedling stage (the com 

 and sugar-cane smuts are exceptions to this) and the mycelium 

 keeps pace with the developing plant, growing sparingly, and 

 without producing any notable symptoms of disease, through the 

 softer tissues. The hyphae are hyaline, branched, sparingly 

 septate, mostly intercellular, with haustoria which enter the 

 cells. When the period of flowering is reached the fungus 

 develops rapidly in the anthers and ovaries and there produces 

 masses of spores (often black and powdery) which replace the 

 pollen and the seeds. In some cases swellings in which spores are 

 produced in a similar way are caused on stems or leaves. 



The spores so formed (chlamydospores) are usually thick- 

 walled and very resistant, in some cases retaining their vitality 

 for many years. They germinate in water, producing a short 

 filament (pro-mycelium) on which elongated thin-walled basidio- 

 spores (distinguished in this family as sporidia) are formed. 

 These are capable of immediately infecting host-plants which are 

 in the susceptible stage. In nutritive solutions, as soil water or 

 moist manure, the sporidia give rise to a yeastlike form of growth 

 which may continue the life of the fungus until a suitable host 

 is encountered. 



Two common types of infection occur in this family, the dis- 

 tinction of which is important in regard to control measures. 

 In certain species the chlamydospores, distributed, after they are 

 set free, in various possible ways but mostly by the wind, adhere 

 to healthy seeds and are planted with them, or are already 

 present in the soil in which planting takes place. They germinate 

 in the soil moisture, producing sporidia, and^these proceed to 



