HtC . 22 , X923 
Cytology of Wheat Stem Rust 
597 
The drainage of the protoplasm from the central mycelium to its 
peripheral hyphae when spore formation begins has been noted by Pole 
Evans ( 12 ) in leaf rust of rye and in other rusts. It may be of general 
occurrence. It is not easy to learn how this transfer of material takes 
place. Of course, it is conceivable that this process involves the actual 
flowing of living protoplasm along the hyphae and through the septa. 
Seifriz (55, p. 281 ), in microdissection of Rhizopus, has shown that its 
protoplasm, particularly in the outer layer, may have high viscosity and 
in occasional filaments the protoplasm is a “firm jelly.” 
By pressure with a needle some distance behind the tprn end (of a hypha) the rod 
of protoplasm can be made to ooze out like oil paint from an artist’s tube. This 
protoplasmic jelly is sufficiently rigid to hold its shape until dissected. 
Of course, this may be no evidence of the consistency of fungous 
protoplasm in general, but it is at least suggestive. It would be difficult 
to understand how viscous materials could pass through the septa 
intervening on the way to the growing tips. Perhaps the contents of 
haustoria and hyphae are reduced by some autolytic or digestive process 
to simpler soluble forms that would be more readily transportable. 
In Mindum only the growing tips of hyphae in older infections show 
stainable contents. All the older hyphae look empty. The first as¬ 
sumption is that the host in some way is poisoning the hyphae. It 
certainly destroys the haustoria, but there is little evidence of positive 
harm done outside of the host cell. In the first attacks of young fungi, 
where the host cell reacts violently, the haustorium mother cell outside 
may collapse. In older infections no visible evidence of injury has been 
detected. It may and probably does occur to some extent, but there is 
no such proof of it, as was seen, for instance, when form XIX was grown 
on Kanred ( 2 ). Many of the hyphae of infections in Mindum are empty, 
but so were those in the central mycelium of this rust on Baart at the 
same age. Perhaps here, too, and by the same process, the contents of 
the hyphae are continually transferred to the growing tips, leaving the 
older hyphae empty. 
It was once believed that the power of a rust to enter a plant was an 
index of its power to infect that plant. Miss Gibson (15) showed that 
germinating urediniospores enter plants quite unrelated to their natural 
hosts, but do not form haustoria. She concludes that— 
it is the power of the hyphae to form haustoria which we must take as an index of 
infective capacity. 
This conception, too, has been modified. In both Mindum attacked 
by form III and Kanred attacked by form XIX haustoria are begun 
but are destroyed by the host, and the fungus fails to become established. 
When form III produces a haustorium in a cell of Mindum, the nucleus 
and part or all of the cytoplasm of the cell flow toward the haustorium 
and surround it. It is not fully proved, however, that the heavy sheath 
about the haustorium of older infections is made of condensed disinte¬ 
grating cytoplasm. 
Other types of sheaths about haustoria have been described. Harper 
(17, p. 664), in studies of Erysipheae, says: 
Innerhalb der Zelle schwillt es (the haustorium) zu einer langliche Blase an, die sich 
fest an den Kern der Wirthszelle anlegt, um endlich von letzterem vollstandig um- 
schlossen zu werden. 
This nucleus becomes disorganized and— 
bildet dann nur eine dicke komige Schicht um das Haustorium. 
