36 BOTANICAL GAZETTE [anvaRY | 
| 
eral special investigations upon the succession of the rust pus- a 
tules, etc., related in the work ‘Die Getreideroste,’’ could not | 
fail to excite suspicion that perhaps the source of disease is an 
internal one, included within the plant itself. : 
How then test whether this suspicion might be right or not? ) 
The first experiments made with this in view showed that , 
8. Wheat plants, which early in the spring, immediately after” 
the melting of the snow, were enclosed in long and large glass tubes — 
stuffed with cotton wool above and below, and consequently care- , 
fully protected against external infection, developed stalks that after 
six to eight weeks showed yellow rust. 
There is no possibility of explaining this outbreak of rust 
through external infection taking place immediately before or : 
after enclosing in the tubes. The immediate sources of the — 
disease in these cases must have been an internal one. Here — 
two possibilities seem to suggest themselves. The first is that— 
in late autumn of the previous year, during early growth of the 
wheat, an external infection came from teleutospores or uredo-- 
spores of the yellow rust, germinating upon the seedlings ; and 
that the fungus afterwards lived a hidden internal life until the 
full outbreak in the spring. The other possibility is that germs 
of disease had been inherited by the seed grain from the paren 
plant itself, 
the growing plants from external infections by raising them 1 
glass houses constructed so that the air could pass in onl, 
through cotton-wool filters. Such experiments in glass hou 
of different construction. have been carried on for four years 
and have shown that i 
9. Plants of a variety of barley extremely susceptible to yellow 
rust, grown in sterilized soil and protected from external infection 
asolated glass houses, have sometimes become rusted. 
These results prove beyond doubt that the disease must : 
come from internal germs inherited from the parent plant. 
