POLLEISr GKAINS I\ THE FRUIT OF THE ASPEN 



927 



(b) Determination carried out by the usual macromethod. 



Niimber of grains investigated ^ 550 

 mgm of pollen investigated = l.fil 



Average value 0.0246 ± 0.0004 



From the above figures it follows that a seed contains an amount of 

 32P present in 0.0246 ± 0.0004 //gni pollen. 



As the weight of one pollen grain was found to be 0.0027 /^gm, one 

 seed had the ^^p content of 8.8 pollen grains, this result being almost 

 the same as that obtained in 1944 (8.3 pollen grains). 



Summary 



Spring aspen branches were placed in a solution containing radioactive 

 phosphate. By this procedure labelled pollen was obtained. 



Female aspen branches were fertilized with the labelled pollen and the radio- 

 activity of the seeds obtained was determined. 



In the experiment carried out in the spring of 1944, one seed was found tO' 

 contain the amount of ^-P present in 8.3 pollen grains. In experiments made in 

 the spring of 1946 the corresponding figure was found to be 8.8. Thus, in the 

 formation of a seed not only the material of the fertilizing pollen grain participates 

 but also that of a further 7 grains. 



Comment on paper 97 



When fertihzing female aspen branches in vitro with ^^p labelled pollen, a seed 

 was found to contain as much ^^p as was present in from 8.3 to 8.8 pollen grains. 

 This at first sight puzzling result suggests the explanation that a fraction of the 

 fertilizing pollen is metabolized, and some of its phosphorus atoms participate 

 in the building up the of seed. The foetus also contains very many more paternal 

 phosphorus atoms than present in the fertilizing sperm. 



