Pole Evans . — The Cereal Rusts. 
447 
the leaf edges and sheaths. The spores are oblong, somewhat pear-shaped, 
spinous, and of a dirty yellow colour. They measure from 18 -27 x 15-19 y. 
It is interesting to note that according to Eriksson and Henning ( 16 ) the 
Uredo mycelium is able to survive the winter. For during 1891-2 fresh 
pustules were produced on the 28th of December, and they continued even 
up to as late as the 28th of March, and during the winter 1892-3 the 
latest and first appearance of fresh pustules was on the 30th of November 
and the 27th of March. 
Also, according to them, the germinating capacity of the uredospores 
falls with the increase in severity of the winter. 
Germination of the Spore. 
From the spore on germination a fine delicate germ-tube runs along 
the surface of the epidermis, and when the tip reaches a stoma, it swells 
up a little into a thin and delicate vesicle, the appressorium. Directly the 
contents have passed from the appressorium into the sub-stomatal vesicle# 
the delicate and now empty appressorium shrivels up and breaks away at 
its junction with the firmer walled sub-stomatal vesicle, and so is rarely seen 
after the formation of the latter. 
The sub-stomatal vesicle is a very definitely shaped body (Fig. 7), 
closely resembling that of Uredo graminis , but narrower. Like that of 
U redo graminis, it gives rise at one end to one infecting hypha only, from 
which the others subsequently arise. In diameter it measures from 4-6 y, 
and in length from 30-35 /i. It differs from Uredo graminis chiefly in the 
fact that the end from which the hypha springs does not cling to the head 
of the guard-cell. 
The resulting hyphae, and especially their haustoria, bear a very 
striking resemblance to those of P. Symphyti-Bromorum. As a general 
rule the hyphae are thinner and more thread-like than even those of P. 
Symphyti-Bromorum or P. simplex. 
The first formation of septa in the hyphae occurs about the third day, 
and always takes place in connexion with the development of haustoria. 
In addition to these septa, others appear at longer or shorter intervals 
in the branched hyphae up to about the tenth day, when, with the pre- 
paration for spore production, the hyphae become drained of their proto- 
plasm and uniform septation occurs in all the older hyphae. So that at 
this stage the only hyphae which are full of contents, and for the most part 
are unseptate, are those which run in the margins of the pustules, the so- 
called ‘ Protomycelium. ’ 
