Dorsey: Pollen Sterility in Grapes 



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WHY SOME POLLEN IS WORTHLESS 



Careful study has shown that in most instances the inefficacy of pollen is due to the 

 fact that the generative nucleus in each cell has degenerated. At the right 

 is a camera lucida drawing of part of a pollen grain of the variety Concord, 

 showing both nuclei normal. The vegetative nucleus, at the top, plays its 

 part in producing the pollen tube, after the pollen grain falls on the stigma 

 and starts to germinate. Down this tube the nuclei formed by a division 

 of the generative nucleus, in the lower part of the figure, will pass, one of 

 which will unite with the egg-cell nucleus to begin the formation of the seed. 

 At the left is shown part of a Brighton pollen grain, in which the vegetative 

 nucleus is normal but the generative nucleus has degenerated. (Fig. 4.) 



determine the nature of this impotency. 

 This has been the subject of some 

 investigations by the writer in the past 

 few years and by careful examination 

 of pollen development in both sterile 

 and fertile forms some interesting facts 

 have been developed. (Dorsey '14.) 



These studies have been carried 

 forward by means of the usual cyto- 

 logical technique and have involved a 

 careful study of pollen development in 

 both the sterile and fertile forms. 

 Particular attention has been given to a 

 study of (1) aborted pollen and (2) 

 the degeneration of the nuclei in the 

 mature pollen. 



It might be well before taking up a 

 consideration of these two topics to 

 state briefly the stages in pollen develop- 

 ment which take place normally. Early 

 in the spring the tissues of the anther 

 differentiate and produce pollen mother 

 cells. These undergo further growth 

 and differentiation, passing through 

 stages well known in the higher plants. 

 The pollen mother cell divides and then 

 divides again, so that we have produced 

 from each pollen mother cell four 

 nuclei. From these, the so-called micro- 

 spores are formed. These young micro- 

 spores, or one-celkd pollen grains, 



undergo a period of growth and en- 

 largement and are finally separated; 

 the nuclei of these pollen grains again 

 divide, forming the mature pollen grain 

 with two nuclei, the smaller one of 

 which is the generative nucleus, which 

 by another division forms the gametes. 



POLLEN DEGENERATION 



Up to the formation of the micro- 

 spores, development apparently takes 

 place normally in the self sterile 

 varieties. We shall consider the 

 aborted pollen and degeneration of 

 the nuclei in the mature pollen. 



The Aborted Pollen: An examination, 

 of the pollen in the mature anthers of a 

 number of varieties, both cultivated 

 and wild, showed that aborted pollen 

 is produced in varying quantities. In 

 some varieties, this amounted to as 

 much as 69% of the pollen produced, 

 while in others there were practically 

 no aborted grains. The aborted pollen 

 was found in both self sterile and self 

 fertile varieties and was produced in 

 practically equal quantities in the wild 

 staminate and pistillate vines of V^itis 

 vulpina. 



No abortion of pollen grains has been 

 noticed in the grape previous to the 



