28 BULLETIN 1328, U. S. DEPARTMENT OF AGRICULTUEE 
It will be noted that the average duration of the voyages was 
determined with a probable error ranging from less than one-half 
of 1 per cent to about 7 per cent, the average probable error being 
2.45 per cent. 
The number of days in the honey flow on which the average dura- 
tion of the voyages could be determined with full confidence in the 
figures was small, owing not only to the fact that the honey flow in 
1922 Avas short but also to the fact that it occurred very early in the 
season, when relatively more difficulties in connection with the appa- 
ratus had yet to be overcome. With changing weather conditions the 
duration of the voyages can be determined more conveniently by the 
graphic method, which, although not so accurate, is correct to about 
3 minutes for the scale used in studying the data. 
A survey of a few days (Table 2) shows that the average duration 
of the voyages varies considerably. The shortest average flight over 
a considerable period of time is that which occurred on April 20, 
8.92 minutes, and the longest that of July 10, 103.92 minutes. Every 
gradation between these limits occurred. It will be noted that during 
the dearth of July the average duration of each flight is much longer 
than during the honey flow ; and yet there are days in July when the 
duration corresponds very closely with such honey flow days as 
May 8 and 9. 
It will be noted also that the duration of the voyages on May 8 
and 9 was from two to three times as long as it was on May 15 
and 17, and yet all four days (Table 1) were days of fairly good to 
good honey flow. This great difference can be attributed only to the 
nature and distribution of the honey plants. On May 8 and 9 the 
bees are working on the black locust {Rohinia pseudacacia) en- 
tirely. The tulip tree (LiriodeiidTon tulipifera) was not yet secret- 
ing nectar. On the 15th and iTth only the tuliptree was secreting, 
the black-locust blooms having been destroyed by a heavy rain on 
the 14th. The distribution of the trees of these two species in the 
immediate vicinity of the hive shows roughly that the black-locust 
trees most accessible are on the average about three times as far 
away as the nearest available tuliptrees. The structure of the flower 
of the black locust undoubtedly also contributes to lengthening the 
average duration of the voyages by requiring a greater exertion from 
the bee in securing its load of nectar. 
The data for May 15, June 6, and July 25 (Table 2) show that 
the duration of the flights may sometimes vary considerably within 
the same day. Under uniform conditions, however, it is usually very 
constant for the greater part of the day's flight. 
Graphs (figs. 11, 12, and 13) have been drawn to show in greater 
detail these variations in the duration of the trips for May 15, a 
day of good honey flow from tuliptree; for July 10, a day in 
the dearth; and for May 9, a honey-flow day with locust secretion, 
with flights of intermediate length. Owing to the heavy flight 
which occurred on May 15, it has been necessary to cut the graph 
into three sections in order to draAV it to the same scale as the graph 
for July 10. These sections should be joined so as to give a con- 
tinually ascending curve such as. is shown in Figure 12 for July 10. 
These curves show that at the commencement of flight the duration 
of the trips is relatively short, soon to be followed by the balanced 
