Pole Evans . — The Cereal Rusts. 
453 
3. Uniform septation of the normal hyphae does not occur as a rule 
until the day before spore formation, so that it is brought about in a com- 
paratively short space of time. 
Nuclei. 
Each nucleus consists of a central body which stains as a deep homo- 
geneous mass with fuchsin, gentian violet, and haematoxylin. 
This central body lies in a clear space, the nuclear zone, and in the 
young and actively growing hyphae, no definite nuclear membrane can be 
made out surrounding it. But in the older hyphae, especially in the long 
runners where the protoplasm is more vacuolated, and the nuclei not quite 
so numerous, the typical resting nucleus is seen. Here it consists of 
a central body lying in a clear area surrounded by a definite nuclear 
membrane, and in some cases connecting strands can be seen running from 
the central body to the nuclear membrane. 
In connexion with the nuclei, which must be in an active state of 
division in the young hyphae, distinct centrosomes can be made out. 
These appear as a single, deep-staining small body just outside the border 
of the nuclear zone. As a rule they are surrounded by a clearer space, but 
no definite membrane or radiations are to be seen (Fig. 15). The nuclei 
divide very rapidly up to the sixth and seventh day, when a change begins 
to take place. Some of them no longer stand out sharply, but they appear 
as dull red specks with no distinct membrane, and there is a great tendency 
for these small and degenerating nuclei to mass together in patches so that 
the hyphae often show a corroded appearance. The surviving nuclei are 
conspicuous by their large size and staining capacity. 
Haustoria. 
The commonest form for P. glumarum is a small club-shaped body, 
which is very frequently seen in close connexion with the nucleus of the 
cell (Fig. 24), whereas the hammer-headed form so frequently met with in 
P. Symphyti-Bromorum is seldom seen. 
The haustoria often contain as many as five nuclei, and attain their 
largest dimensions in the cells surrounding the vascular bundles, where they 
are usually very numerous and much branched. In no case have they been 
seen in the vascular elements themselves. 
As the haustoria become older, they become very thick walled, and 
have an empty or very vacuolated appearance, while the wall stains very 
deeply and the nuclei can no longer be made out. Arborescent forms, such 
as are shown in Figs. 18 and 19. are frequently found. 
Preparation for Spore Formation. 
Towards the eighth day the hyphae become very vacuolated, contain 
fewer nuclei, which are frequently of an oval shape and stain very deeply. 
