Originally communicated in Arkiv Far Kemi, 23 B, 5 (1946). 



97. NOTE ON THE NUMBER OF POLLEN GRAINS 

 IDENTIFIED IN THE FRUIT OF THE ASPEN 



C. Eklundh-Ehrenberg, H. Eulee, and G. Hevesy. 



From the Institute for Research in Organic Chemistry, Stockholm 



The atoms of paternal origin present in the offspring are not confined 

 to the atoms of the fertihzing sperm. The constituents of the numerous 

 spermatozoa ejaculated into the female organism are absorbed and 

 subsequently partly incorporated into the foetus. Do excess pollen 

 grains contribute in a similar way to the formation of the seed, and, 

 should this be the case, to what extent ? 



In order to clear up this point we produced aspen pollen containing 

 radioactive phosphorus, fertilized female aspen with this and determined 

 the radioactive phosphorus content of the seeds obtained. 



EXPERIMENTAL 



Three aspen branches were placed shortly before the formation of pollen in 

 glass cylinders each containing about 20 ml of a 0.5 mM sodium phosphate solution 

 of 1 millicurie activity. 



The labelled phosphate diffused into the branch and participated in the for- 

 mation of pollen. Strongly active pollen was obtained after the lapse of 7 days 

 emitting several /9-par tides per microgram of pollen. 



It was of importance to add the labelled phosphate to the solution containing 

 the branch before the formation of pollen, as the uptake of ^^p by already existing 

 pollen is very restricted. 



That preformed leaves take up appreciable amounts of ^^P is seen in Fig. 1. 

 which shows the radioautograph of a leaf on a branch placed in the active solution 

 for 8 days. The leaf, after removal from the branch, was placed on a film covered 

 with a thin layer of cellophane and held in position by a heavy glass plate. After 

 the lapse of 2 days the fihn was developed. Fig. 2 shows the radioautograph of 3 

 leaves which were largely grown after the uptake of radioactive phosphate by the 

 branch. 



Knowing the activity of 1 microgram pollen and the number of pollen grains 

 weighing 1 microgram, we can calculate the activity of a single grain. 



After collecting the fruits about 3 weeks after fertihzation, we determined 

 the activity of a known number of grains. 



From the ^^P content of a seed and that of a pollen grain, we can calculate 

 the number of grains whose ^-P content participated in the formation of a seed. 



