20 Director’s REPORT OF THE 
suggestions as to the location and construction of fumigation 
houses or chambers. 
Spraying fruit trees in bloom.—The effect of spraying fruit trees 
when in bloom with the common insecticides and fungicides 
which are used in orchards has been under investigation during 
the past season. The work was carried on both in the labora- 
tory and in the orchard. In the laboratory the germination of 
pollen grains and the growth of pollen tubes in cultures which 
contained none of the poisons used in spray mixtures were coin- 
pared with the germination and growth in cultures which con- 
tained either some insecticide or some fungicide, or both. 
In these cultures both the Bordeaux mixture and copper 
arsenite of the strength commonly used in spraying apple orch- 
ards practically prohibited the germination of the pollen grains 
with which they came in contact. In cultures containing but 
2 per ct. of the 1-to-11 Bordeaux mixture pollen germination 
occurred only in rare cases; while even the presence of only 1 
per ct. of this mixture had a decidedly adverse influence on 
the germination of pollen and the development of pollen tubes. 
In the field investigation an effort was made to learn what 
effect the spray mixtures have upon (a) the essential organs of 
the flower, (b) upon the yield of fruit and (c) upon the fungous 
diseases and insects which are injurious to the crop. 
In almost all cases where the blossoms were hit in the center 
by the spray they failed to set fruit. In some cases the spray 
caused the stamens and pistils to wither prematurely. Oc- 
casionally when the spray hit the stigmatic surface the pistils 
remained green for an unusually long time awaiting pollination, 
but at last they withered and set no fruit. The laboratory cul- 
tures showed that the pollen could not grow in the presence of 
even quite dilute spray mixtures. It seems, therefore, that the 
spray mixture on the stigmatic surfaces, in the cases just cited, 
by preventing the growth of any pollen which may have reached 
the stigmas caused the blossoms to fall away without setting 
fruit. 4 
