502 
On Wheat Mildeic. 
Fig. 6. — Spore of the 
Mildew of Wheat ger- 
minating and produc- 
ing Spores at the Tip 
of one of the Branches. 
appropriates the material which was intended to build up the 
growing wheat. But as the wheat at the time of the attack is 
very active in assimilating food, the 
rust rarely injures to any serious extent 
the crop, unless in an exceptionally 
wet season, when the abundance of 
moisture secures the germination of suc- 
cessive crops of spores. A few bright 
sunny days arrest the progress of the 
fungus, and vigorous plants overcome 
the attack without any real injury. 
When, however, the mildew appears 
at a later stage in the life of the wheat, 
the conditions are entirely changed. 
The period of active assimilation of 
food is past. The plant has laid up 
stores of food in various parts of its 
structure, and the processes of flowering 
and fruiting, which use up these stores, 
are proceeding. The altered starch is 
being conveyed from the cells, where 
it was temporarily located, to its final 
destination in the seed. The fungus 
arrests it in its progress, and converts 
it to its own use. The wheat is not 
able to cope with the parasite as in 
the earlier stage of its life when the 
fungus was present as rust. It cannot 
start again the process of assimilating 
food, and consequently the seed is 
more or less imperfectly filled, in 
proportion to the time at which the 
fungus attacks the plant, and the extent of the attack. 
The story of the fungus suggests important considerations to 
the farmer. First, it is certain that the brown spores of the 
mildew which remain attached to the straw after harvest, are 
the means by which the fungus retains its vitality through the 
winter. Converting the straw into manure does not destroy 
the spores, but rather provides in the spring the conditions 
fitted for their germination. It may be recommending a serious 
destruction of property to suggest the burning of mildewed 
straw, but fire is the only agent that will effectually destroy the 
spores. 
Then it should be noted that even the brown winter spore 
produced by the mildew will be harmless, unless the spores 
formed at the tips of its branches in the spring rest on the leaf 
