10 BULLETIN 542, U. 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 insignificant. 



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 grains 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 ring 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. Following 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. Dcr Einfluss der Luftfeuchtigkcit auf die Lebensdauer des Bliitenstaubes. In Jahrb. 

 Wiss. Bot.,Bd. 47, Heft 1, p. 6-33. 1909. 



