252 PUCCINIA 
trivialis, Secale Cereale, Trisetum flavescens, Triticum vulgare. 
These are the British grasses among those recorded by Sydow ; 
the teleutospores have not been found, and probably do not 
occur, on all these in this country. (Figs. 193, 194.) 
This is the famous “rust” (uredo-) or “ mildew” (teleutospores) of corn 
about which so much has been written. But all the earlier observers 
confused together the various rusts of Cereals of which a number are now 
distinguished. P. 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, 4—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 mavy parts of England now than some of the following species. 
Whether this is due to the general extirpation of wild Barberry bushes or 
not, is not certain ; at any rate they are very uncommon, and the ecidium 
on the cultivated species of Berberts 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 
eecidia 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 Metdiwm graveolens 
Shutt]., which was formerly wrongly identified with <. 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. dispersa 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 does the greatest harm to the crops; it is reported 
to cause much loss 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 be 
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 
