97 
may be quite a number of generations in the course of a vear. Some 
freshly-laid eggs of this species, gathered January 13 and placed 
under glass, hatched about eighteen days later. 
Mr. Green made experiments to determine the food preferences 
of the larvre. A cucumber plant \vas potted in clean sand, and 100 
of the maggots were placed about its base. These affected the 
plant, the stem being evidently eaten by them. The same experiment 
was made with the addition, at one side of the pot, of a cubic inch 
of decayed horse manure, such as is mixed with earth in growing 
cucumbers. The larv?e were subsequently found collected about the 
piece of manure and the plant remained uninjured. Next a plant 
was potted in a mixture of manure with earth from the forcing beds 
infested by maggots. The plant was not injured. These experi- 
ments, although on too small a scale to be decisive, confirm the 
supposition that the maggots feed preferably on decaying manure, 
injury to the living plants resulting only in case the larv?e are ex- 
cessively abundant. 
A very careful and extended study was made by Mr. Green 
of the history of infested beds at Dixon and Morrison, with espe- 
cial reference to the source and treatment of the manure mixed 
with the earth used in making up cucumber beds. Severe infesta- 
tion invariably followed the use of fresh horse manure in fall. 
For example, in one case beds w^ere started in the fall with soil from 
an old pasture mixed with fresh horse manure. When the plants 
were about five inches high they suddenly wilted and all died, and 
the flies soon came out in such numbers as to cloud the glass in the 
houses. The whole place was thoroly cleaned and whitewashed, 
and a new start was made with more manure from the same source 
and earth from a nearby cultivated field. Serious injury again 
followed, and the flies became as thick as before. 
In another case manure was collected from livery barns, and in 
late summer and fall some fresh manure was added, also soil from 
river alluvium and old land, and the beds were started with the 
mixture. Four weeks later the plants began to v>^ilt and about 
three-fourths of them died. In a similar case as to material used 
the soil was steamed three hours, but without apparent effect, as 
the flies became very thick and about 50 percent of the plants 
were lost. 
When the manure used was gathered in winter or early sum- 
mer and well rotted before using, little or no injury followed. 
In another class of instances, where the manure used was com- 
posted with lime, no injury resulted unless, as was frequently the 
case, fresh manure was added to make up a deficiency, when the 
injury varied with the amount of fresh manure used. In one case 
the infestation was slight at first, but reached serious proportions 
by the next spring. In another case the additional fresh manure 
