532 WISCONSIN FRUIT-GROWERS’ ASSOCIATION. 
Some species of parasitic fungi are known to flourish most 
in dry weather, others require moisture for their rapid develop¬ 
ment. Again, if we sow peas in spring or early summer, they 
will probably carry their crop to perfection without exhibiting 
any signs of mildew; but sow peas towards mid-summer, and 
the probability is, that the plants will be destroyed by mildew. 
This is the case in England, and I find it is so here. On the 
contrary, if we sow turnips or rutabaga in the spring or early 
summer, they are almost sure to be mildewed; the lower leaves 
will perish one after another, and the roots generally become 
more or less decayed; but sow seeds of these plants sometime 
a''ter mid-summer, and the chances arc that we shall have a 
healthy crop free from mildew. 
The disease of the pear tree, which renders the raising of 
pear seedlings for stocks, so difficult in the Eastern States, is 
probably the work of a parasitic fungus. I ventured to make 
this suggestion in the Horticulturist , in the time of Mr. 
Downing, and advised that diseased leaves should be submitted 
to botanists distinguished for their knowledge of these plants, 
for their opinion; and I find by a late nnmber of Lindley's 
dardiner's Chronicle , that a gardener in Pennsylvania has 
consulted Mr. Berkely on the subject, who decides that the 
destruction of the leaves is caused by a fungus. Mr. Berkely 
ranks first of all British botanists, for his knowledge ot these 
plants, and to him belongs the merit of proving that the para¬ 
sitic fungus, named and described by him as Botrytis infestans 
is the immediate cause of the potato disease. Thirteen years 
have now elapsed since his observations were published. His 
conclusions were supported by the independent testimony of 
equally competent observers in other countries, and the expe¬ 
rience of every subsequent year, has tended to confirm the 
accuracy of the conclusions at which he had arrived. Yet, 
notwithstanding all this, so little seems to be generally known 
respecting the action and power of these insects, that a genera¬ 
tion will seemingly have to pass away, before even the conduc¬ 
tors of farm journals, to say nothing of farmers generally, will 
