62 TYPES OF BRITISH PLANTS 
may thus become affected, and, which is even worse, it 
may sink to the ground and make a home in the potato 
tuber beneath. If these are used for seed in the 
next year the disease is certain to reappear and take an 
unshakeable hold upon the plant. 
On the other hand, while some of the funguses are thus 
destroying what is useful to mankind, others are trying 
to keep down some of his pests. Potatoes may be 
killed by the fungus, but cabbages are being gnawed 
through by the caterpillar of the Cabbage White Butter- 
fly, so, as some compensation, another fungus makes an 
onslaught on the caterpillar and completely fills it with 
its branching tubes. The common House Fly, after 
annoying everyone during the summer, often in the 
autumn pays the penalty to a third small fungus, which 
completely envelops the fly in a halo of its fruits, as you 
may see for yourselves if you examine dead flies about 
that time, especially those you may find on the window- 
panes, where they go for rest, and are fastened down by 
the sticky cords of the fungus. 
The Mildews, Smuts, and Rusts we must leave, for our 
space is not sufficient to deal with all these pests of the 
farmer, but with them, as with most other fungi, there is 
one thing worth remembering. What you see of them, 
either the black smut in the wheat ear, the mildew on an 
apple tree, or what not, is the fructification only of the 
plant. The mischief is being done, and all these fruits 
are being produced, by the thread-like tubes running all 
in and out among the cells and tissues of the host, and 
sucking out its life-blood. Many curious excrescences on 
plants are the effect of a fungus invasion. You may 
know the “ Robin’s Pincushion” on wild roses. This is 
the result of a fungus invasion, which has stimulated the 
— ., 
-* bill zal 
