10 BULLETIN 542, L T . S. DEPARTMENT OF AGRICULTURE. 
PROPORTION OF PERFECT AND ABORTIVE POLLEN GRAINS. 
On examination of the pollen of one variety in January it was 
found that some of the pollen grains were either small or appeared to 
be empty. Following up this observation, an attempt was made to 
determine whether the proportion of poor grains was larger in unpro- 
ductive varieties than in productive ones and whether this question 
might have any bearing on the productiveness of a variety. 
Early in the season a much larger proportion of poor pollen was 
found than later on, when the weather was warm and the flowering 
normal. At the latter time no variety was found in which the num- 
ber of defective pollen grains would average over 8 or 10 per cent at 
the highest, and usually it did not average more than 2 to 4 per cent 
of the total. The number varied greatly in different anthers of the 
same variety; thus, in the Bennett as much as 25 per cent of empty 
grains was found in one anther, but this was exceptional and the 
number of poor grains normally found in this variety was ^significant. 
Defective pollen grains are of two kinds : (1) Those which are under- 
sized and (2) those which are empty and appear as irregular, col- 
lapsed bodies of a darker color when seen under the microscope. 
Frequently there is considerable variation in the size of the pollen 
grams, many being somewhat smaller than normal and a few being 
very small. The average of every variety, however, shows a very 
small proportion of grams which are abnormal in appearance, the vast 
majority being uniform in size and shape, plump, and apparently 
perfect. 
ARTIFICIAL CULTURE OF THE POLLEN GRAINS. 
The method used in the artificial culture of the pollen grains was 
that of Max Pfundt. 1 On a glass slide a small glass ring was mounted ; 
a drop of the culture medium was then placed on a cover glass and 
this inverted over the ring, the edge of which had been previously 
greased with vaseline to exclude the air. The bottom of the chamber 
inclosed by the glass rhig was covered with the culture solution in 
order to keep the vapor tension within the chamber as uniform as 
possible and to avoid the slightest change in the concentration of the 
hanging drop. Pollen was sown upon this hanging drop, previous to 
placing it over the glass ring, by taking a stamen upon which pollen 
was freely exposed, holding it in the forceps, and lightly touching the 
surface of the drop in several places. The culture thus prepared was 
labeled and between observations placed in a large glass moist cham- 
ber. Folio whig the method of Pfundt, this moist chamber was kept 
in the dark. 
A considerable amount of experimentation was necessary before 
a successful culture medium was obtained. Cane-sugar solutions 
1 Pfundt, Max. Der Einfluss der Luftfeuchtigkeit auf die Lebensdauer des Bliitenstaubes. In Jahrb. 
Wiss. Bot., Bd. 47, Heft 1, p. &-33. 1909. 
