■2'rl PUCCINIA 



trivialis, Secale Cereale, Trisetum flavescens, Triticum vulgare. 



These ;ire t li> • British grasses among those recorded by Sydow : 

 the teleutospores have not been found, and probably do nol 

 occur, on all these in this country. (Figs, lit:;. 1!)4.) 



This is the famous " rust " (uredo-) or "mildew" (teleutospores of corn 

 about which so much has been written. But all the earlier observers 



(.•ont'usoil together the various rusts of Cereals of which a number are now 

 distinguished. /'. graminis is known as the "Black Rust," on account of 

 the dark colour of the teleuto-sori : these are very distinctive, forming 



narrow black lines, | — 1 cm. long, chiefly on the sheaths and culms. 

 However abundant this species may have been in the past, it is much less 

 common in many parts of England now than some of the following species. 

 Whether this is due to the general extirpation of wild Barberry hushes or 

 not, is not certain ; at any rate they arc very uncommon, and the avidium 

 on the cultivated species of Berberis and Mahonia is rarely met with in 

 England. 



The test by which alone the Black Rust can be absolutely distinguished 

 is the power possessed by its basidiospores of producing the characteristic 

 secidia on the Barberry. There is a European but possibly non-British 

 species of Puccinia (P. Arrhenatheri) which has also the Barberry for 

 its alternate host, on which it produces peculiar " witches'-brooms," the 

 mycelium living perennially in the twigs. This is JEeidium graveolens 

 Shuttl., which was formerly wrongly identified with /E. magelhaenicum 

 Berk, from Tierra del Fuego. 



The uredo-stage of P. graminis can generally be recognised in the field 

 by its sori, which may reach a length of 10— -15 mm. and are of a rusty- 

 orange or brownish-ochre colour ; they do not become general till the 

 beginning of June. Forms of P. disperse/, are often mistaken for it. 



Microscopically, the uredospores are seen to be longer compared with 

 their breadth (more ellipsoid) than is the case with the other cereal 

 species ; the teleutospores, which germinate only after a winter's rest, are 

 longer and have longer pedicels ; their sori form much more conspicuous 

 lines and do not remain for long covered by the epidermis. It is the 

 uredo-stage which dees the greatest harm to the crops ; it is reported 

 to cause much less in the United States, South Africa, Australia and 

 Tasmania, but not much in India. 



This species has been divided by Eriksson into six biological races, 

 but they are of a very indefinite character and later researches (see 

 Carleton, '99, p. 52) throw grave doubt upon their reality. At any rate, 

 they are not the same in America as in Europe, though this may he 

 explained by supposing that, since these forms are undergoing evolution 

 at the present moment, the course of this evolution is different in America 

 from what it is in Europe. The existence of these races is, however, 

 important; they show that the wheat cannot necessarily be infected by 



