246 



The Journal of Heredity 



^P 



NORMAL GRAINS OF GRAPE POLLEN 



At the left, photomicrograph of a quantity 

 of potent pollen grains from the vari- 

 ety Clinton, mounted in lactic acid; 

 at the right, external view of the 

 suture and germ-pore of fertile pollen 

 from a staminate vine grape of the 

 wild-river bank ( Vitis vulpina). Each 

 yjollen grain, when dry has three longi- 

 tudinal folds or sutures in the thick 

 outer covering and when it is put in 

 water these unfold and the grains 

 often become twice as large as when 

 dry. (Fig. 3). 



normal fertile pollen. The normal pol- 

 len is oblonj^f in outline with slightly 

 flattened ends when dry, while the 

 sterile is quite irregular and folded. 

 By careful experiments he showed that 

 the irregttlar grains, whether occurring 

 mixed with the normal grains or not, 

 failed to germinate when placed in a 

 nutrient sugar solution. As a result of 

 this work it is jjossible to tell whether a 

 new variety is self sterile by means of a 

 microscopic examination of its pollen. 



Flower Types: As is well known, 

 there occur in the grape three types of 

 flowers, (1) those with stamens upright 

 and jjistils abortive (this type of flower 

 is functionally staminate), (2) those 

 having ui)right stamens and pistils 

 fully develoiK-d and functional (the 

 IxTfcct flowers), and (3) those with 

 reflexcd stamens containing sterile pollen 

 and fully developed jnstils (functionally 

 the pistillate flowers). While the culti- 

 vated varieties quite generally produce 

 functional ])istils, there arc, however, 

 occasional vines found which have only 

 a partial development of the ])istil. 

 The writer ('12) showed that, with 

 resiject to pistil deve'lopment, prac- 

 tically a complete series of intermediates 

 occur between those forms which are 



classified as staminate and those classi- 

 fied as pistillate. 



A classification based upon stamen 

 type, of 132 important commercial 

 varieties, shows that there are ninety- 

 five varieties with upright and thirty- 

 seven with reflexcd stamens. Of the 

 ninety-five only eleven are classed as 

 self sterile or partly so, while only 

 two of the thirty-seven ha^■ing reflexcd 

 stamens were partly fertile, the re- 

 mainder being sterile. 



SUMMARY OF RESULTS 



These results may be briefly sum- 

 marized as follows: (1) Self sterility in 

 the grape is due to the pollen. (2) All 

 varieties tested set fruit when ])otent 

 jjollcn was used, which shows that the 

 pistils arc normal. (3) Certain varie- 

 ties are more effective as pollcnizers 

 than others. (4) When dry, potent 

 pollen can be distinguished from im- 

 potent by its shape. (5) Impotent 

 jjollen is correlated with the reflexcd 

 type of stamen. 



The Nature of Sterile Pollen in the 

 drape: It will be interesting, now, 

 since it has been shown that the ])()llen 

 Ijornc by a number of American \-aricties 

 of grapes is more or less impotent, to 



