276 USTILAGINEAE. 



the resting-spores are developed that deformation occurs. These 

 spores arise by intercalary growth in the mycelium, which is 

 generally completely used up in their formation; they are 

 produced in large numbers, and scattered after decay of the 

 tissues enclosing them. 



As a result of the germination of the resting-spores, there 

 is produced either a mycelium capable of immediate infection, 

 or a promycelium from which conidia^ are abjointed. In the 

 latter case, conidia are generally formed in succession, and 

 continue to be given off from the promycelium for a considerable 

 time. They either give out a germ-tube capable of infecting a 

 new host, or give rise to further conidia. The latter process 

 is most frequently observed in artificial nutritive solutions, 

 where the conidia continue to sprout in a yeast-like manner 

 till nourishment is exhausted, when they germinate and form 

 mycelial filaments. In the host-plant, chlamydospores alone 

 are developed, conidia exceptionally {Tiiburcinia and Enty- 

 loma). 



The Ustilagineae are very dangerous and injurious enemies 

 of cultivated plants, especially to the various cereal crops. The 

 species are fairly easy to identify, because each is, as a rule, 

 confined to one or a few species of host. The smut-fungi are 

 best combated by sterilizing the seed of suspected cereals in 

 a copper sulphate solution or in hot water shortly before 

 sowing out; (see General Part, chap, vi.) In this way any 

 adherent smut-spores are killed, and where this preventive 

 measure is regularly carried out, disease is less common and 

 its effects considerably minimized. 



The Ustilagineae include the following genera : Ustilago, 

 Sphacelotheca, Schizonella, Tolyposporium, Tilletia, Entyloma, 

 Melanotaenium, Urocystis, Tuhurcinia, Daossansia, Schroeteria, 

 Thecaphora, Sorosporium, Graphiola, Schinzicc, Tithercularia. 



Ustilago. 



The vegetative mycelium makes its way through the tissues 

 of the host-plant without causing any deformation. The spores 

 are developed in certain parts of the host, and form a much- 

 branched, compact, sporogenous mycelium, with membranes 



^ ' Conidia ' = the sporidia of De Bary. 



