93 
A remarkable point is the sudden progress of the disease. First the 
tip of the stem is seen hanging slack, aud two or three days after the 
whole stem above the said sick spot is dead. In 1891, when I repeatedly 
received seudings of sick Clematis stems. I did not succeed in discov- 
ering the cause of the evil, though I could not help supposing that I 
had to do with the mining of a very small larva, for I discovered in the 
affected spots mines, which I could hardly consider to be the effect of 
the work of the nematoid worms I had found; but I did not discover 
the likeness of a larva or nympha. 
In 1892 I was more successful. That year the stems were sent me 
in June. I then found on the affected spot, in the midst of the 
stem, a very small larva of a fly; in some already a brownish nympha 
with a thin, very perishable film. About the middle ol June out of 
these nyinphse came the little fly Phytomyza affinis Fall., which conse- 
quently must be considered to be the cause of the disease. All the 
above-mentioned symptoms of sickness, which, at first sight, seemed 
rather enigmatical, were most satisfactorily explained. I further found 
that of Phytomyza affinis two generations at least are born every year. 
Therefore, as soon as the disease makes its appearance (in early sum- 
mer), all decaying stalks must be cut off and burned, lest the evil grow 
worse by the birth of a new generation. 
Mr. Hopkins reported having observed a disease of potatoes due to 
mines somewhat like those described in this paper. 
Mr. Grarman spoke of minute mines in the terminal twigs of apple 
trees, accompanying a sudden blighting of the twigs, which he thought 
might be due to some related insect. 
The following paper was then read : 
FARM PRACTICE AND FERTILIZERS AS INSECTICIDES. 
By John B. Smith, Sc.D., New Brunswick, X. J. 
It is safe, I think, to assume that every economic entomologist has 
been at times woefully disappointed at the outcome of what seemed the 
most promising experiments. Most of us have learned by sad experi- 
ence that because a poison, or one used as such, acts well in one instance 
we can not be at all certain that it will act equally well in another. 
Many of us have run across insects that seem to eat all our usual insect- 
icides with perfect impunity, or upon whom they act so slowly that they 
are practically of no effect. I ha ve in mind at present, from my own 
experience, the Rose chafer, Maerodactylus subspinosus, of which many 
farmers claim, from experiment, that the arsenites do not injure it. I 
am not quite ready to agree to this, but I am certain that they act so 
slowly as to be useless. 
Frequently we find insects whose life habits are such that we can not 
