240 
Journal of Agricultural Research 
Vol. XXVII, No. S 
METEOROLOGICAL RELATIONS 
The meteorological data used in this study are those for Washington, 
D. C., and were procured from the United States Weather Bureau. 
That temperature, rainfall, and sunshine are intimately associated with 
the blooming of wheat flowers appears evident from a consideration of 
figure 2. Temperature, however, seems to be the most important of 
the meteorological influences affecting blooming. The two days show¬ 
ing the most significant relation between temperature and flower bloom¬ 
ing are May 15 and May 16, when almost perfect sunshine with no 
rainfall was registered. On these two days 60.8 per cent of all the 
flowers bloomed. Maximum blooming occurred on May 15 and 16, 
when the temperatures were 76° and 78° F., respectively. Active 
blooming usually begins shortly after sunrise, on days with clear skies, 
and anthers in flowers opening on these days dehisce more rapidly than 
those in flowers opening on cloudy days. Cloudiness or rain has the 
effect of retarding blooming, principally through the lowering of the 
temperature to a point below the optimum for this process. On cloudy 
or rainy days, however, when the temperature is favorable for blooming 
the flowers either open incompletely or bloom cleistogamously. On 
May 18 flowers were observed opening in a drizzling rain and pollen 
was shed from the anthers. No flowers were observed to open at any 
time during a rain of such intensity as to permit droplets of water to 
adhere to the glumes. 
Three periods of intense blooming were noted: (1) On May 14 
between 5 and 6 p. m., (2) on May 15 between the hours of 9 to 10 
a. m., 1 to 2 p. m., and 3 to 4 p. m., and (3) on May 16 between the 
hours of 9 to 10 a. m., 1 to 3 p. m., and 5 to 6 p. m. The weather 
conditions on May 15 and 16 were very similar, and it is interesting to 
note the consistent correspondence of the three periods of intense bloom¬ 
ing on these two days. The single period of intense blooming on May 
14 apparently corresponds to the third period on May 15 and 16. On 
both the latter days a larger number of flowers bloomed in the second 
or middle period than in the first or third periods, which are of approx¬ 
imately the same intensity. The interval between the first and second 
blooming periods of these two days is approximately twice as great as 
between the second and third periods. 
Fruwirth (2), of Austria, states that when the temperature at 4.30 
a. m. is above 14 0 C. the blooming begins at this hour. Many flowers 
bloom from this time to 5.30, while from 5.30 to 9 the number is less. 
Very many bloom from 9 to 10 a. m., while very few bloom from 10 
a. m. to 2.30 p. m. From 2.30 to 3.30 p. m. the number again is large, 
while from 3.30 to 7 p. m. it again is small. The principal blooming 
time of the morning, made up of a preceding and succeeding period 
of which the first or the second may be the stronger, is followed in the 
afternoon by a later blooming period which approaches in intensity the 
weaker part of the morning blooming time. 
On May 17, when lower temperatures prevailed, the only period of 
intense blooming was between 11 a. m. and 12 m., while on May 18 
two periods occurred, one from 3 to 4 a. m. and one from 10 to 11 a. m. 
The intense blooming on May 14, 15, and 16 exhausted the flowers 
available for blooming to such an extent that with unfavorable atmos¬ 
pheric conditions on the 17th and 18th (cloudiness, rainfall, fluctuating 
temperature) only irregular blooming occurred on these days. 
