446 
Pole Evans . — The Cereal Rusts. 
these species and those to be described below, is that it always occupies 
a definite position relative to the stoma, i.e. in Uredo graminis and most 
other species its long axis is always parallel to the stomatal slit. From 
one end of the substomatal vesicle the infecting hypha is given off, which 
at once penetrates the host cells by means of its haustoria (Fig. 3), and thus 
a successful infection of the host is accomplished. 
A very characteristic feature connected with the substomatal vesicle of 
this species is that the end from which the infecting hypha springs always 
clings very closely to the head of the guard cell, or the epidermal cell 
abutting on it. 
From the position of the organs depicted in Figs. 2 and 3 it will be 
clear that the complete sequence of infection, as has usually been figured, 
cannot be attained by transverse section ; for the relative position of these 
organs is such as to make this almost impossible with anything like 
moderately thin sections. In Fig. 4 is shown such a transverse section, 
which happens to pass through the point of union of appressorium and sub- 
stomatal vesicle. 
In diameter the appressorium is 9 /x, while in length it is roughly 27 [j., 
the substomatal vesicle being approximately of the same dimensions. The 
hyphae are of uniform size, and measure 3*5 /x in thickness. 
The haustoria are very varied in shape. They attain their greatest 
development in the cells bordering on the vascular bundles, where they 
often become very branched and contorted. A very young haustorium, 
which has just penetrated one of the mesophyll cells, is seen in Fig. 5, 
while in Fig. 6 forms commonly found in the epidermal cells are shown. 
Puccinia Phlei-pratensis , Erikss. and Henn. 
The Timothy rust was set apart from P. graminis in 1894 by 
Eriksson and Henning ( 16 ) as a distinct species, because out of ninety-two 
infections with good germinating material on Berber is, only one feeble 
infection resulted. From this they concluded that this form does not 
probably form its aecidium on Berberis . 
Further experiments on Berberis by Eriksson ( 10 ) ( 14 ) have simply 
served to confirm this result. He has also shown that it can be transferred 
in the Uredo stage from Phleuni pratense to Festuca elatior and vice versa 
(Eriksson) ( 9 ) ; and in addition that it will feebly infect Phleam Michelii , 
Secale cereale , and Avena saliva (Eriksson) ( 14 ), but does not infect Triticuni 
vulgar e , Hordeum vulgar e , and Poa pratensis . 
Consequently Eriksson regards P. Phlei-pratensis as ‘ nicht scharf 
fixiert ’. 
P. Phlei-pratensis is distinguished in the Uredo stage by the dark 
yellowish-brown pustules which are from 1-2111111. long; these may fre- 
quently run together in a long line as much as lo mm. long or more on 
