40 BULLETIN 1450, U. S. DEPARTMENT OF AGRICULTURE 
ally cross-pollinated. Results obtained in experimental breeding 
support the theory that cross- fertilization of timothy does take place 
to some extent. On the other hand, it is not wholly self-sterile, 
since when the heads of any plant are inclosed in a paper sack 
during the blooming period some germinable seed is usually ob- 
tained, though a much smaller proportion of the florets produce 
seed than when pollination occurs under normal conditions (IS, 
p. 289-293). 
The florets growing in the upper part of a timothy head bloom 
first. Florets lower on the head come into bloom on succeeding 
days, the last to bloom being those growing near the base. The 
florets on a single head may continue to bloom during about 6 to 
16 days. Timothy heads at different stages of bloom are shown in 
Plate 9. 
Timothy florets begin to bloom in meadows of ordinary timothy 
in northern Ohio about June 15 or 20 and continue to bloom in 
large numbers until about July 10 or 15. The period during which 
florets are blooming in very large numbers, however, is about 10 
days, most frequently from about June 25 to July 4, but varying 
a few days from this time, earlier or later, in some seasons. When 
weather and soil conditions are favorable for the development of 
shoots with heads during the late summer and fall, florets may 
bloom in relatively small numbers until late fall. 
The greatest number of timothy florets bloom in the early morn- 
ing hours, from about midnight until about the time of or soon 
after sunrise. The number of florets that bloom each day and also 
to some extent the time of blooming are affected by weather condi- 
tions, especially temperature. Clear weather and a minimum daily 
temperature of 60° F. or above are most favorable. When the 
weather is relatively cool, and especially if it is cool and cloudy or if 
there is a rainfall, timothy florets frequently fail to bloom. 
When timothy florets do not bloom on any particular day they 
are likely to bloom in large numbers on the day following, even 
though conditions are not most favorable. Thus on the morning of 
June 28, 1919, the sky was clear; the temperature during the 24 
hours preceding 8 a. m., at the United States Department of Agri- 
culture Weather Bureau station at Cleveland, Ohio, which is at a 
distance of 22 miles and at approximately the same elevation as the 
timothy-breeding field station, ranged from 56° to 66° F. ; no 
timothy florets bloomed on that morning. On the morning of June 
29, when the sky was again clear, timothy florets bloomed in medium 
numbers, though not in so large numbers as on some days, so that 
the meadows appeared somewhat purple in color, even though the 
temperature during the preceding 24 hours ranged from a minimum 
of 52° to a maximum of 61° F. When weather conditions remain 
very unfavorable, however, timothy sometimes fails to bloom for 
two days in succession. 
Except when unfavorable weather conditions exist, the blooming 
of timothy may be regarded as a process continuing without inter- 
ruption from day to day from the beginning to the end of the 
blooming period. This is illustrated by records obtained daily in 
1921 from June 20 to July 3, inclusive. The minimum daily tem- 
perature during this period at the Cleveland Weather Bureau sta- 
